WO 2007/104072 PCT/AU2006/001415 1 "A MOBILE ACCOMMODATION UNIT" FIELD OF THE INVENTION This invention relates to a mobile accommodation unit. In 5 particular, the invention relates to a caravan and therefore will be described in this context. However, it should be appreciated that the invention may relate to powered vehicles that incorporate accommodation such as motor homes or recreational vehicles. BACKGROUND OF THE INVENTION 10 Caravans and motor homes are a very popular form of temporary accommodation in the western world. Every holiday time, many thousands of people tow their caravan to a favourite holiday destination. The popularity of caravans is largely due to the features that a caravan is able to supply. Many caravans supply all of the comforts of home including a toilet, 15 a shower, a kitchen, dining facilities and beds. Typically, caravans that supply luxurious features are very large. This makes these types of caravans difficult to tow due to their length and weight. Further, caravans that include these features cannot be taken off-road due again to their length,height and weight. Hence, people who 20 want to go to remote places normally do not purchase this type of caravan. Off-road caravans typically provide minimal features such as a small bed and some kitchen appliances. This is because they must be small in order to be towed through rugged terrain. Off-road caravans enable people to travel to more remote places with a level of comfort. However, 25 people who would like all the comforts of home do not typically purchase off road caravans. OBJECT OF THE INVENTION It is an object of the invention to overcome and/or alleviate one or more of the above disadvantages or provide the consumer with a useful or 30 commercial choice. SUMMARY OF THE INVENTION In one form, although not necessarily the only or broadest form, WO 2007/104072 PCT/AU2006/001415 2 the invention resides in a mobile accommodation unit comprising: a base and a top; the top being able to be moved telescopically with respect to the base between an open position and a closed position; and 5 a bed assembly being movable between an extended position and a retracted position from either of said top and said base; wherein the bed assembly is movable to an extended position when the top is in an open position. Preferably, the bed assembly includes side flaps that are 10 foldable. The side flaps may be folded when the top is moved to a closed position. In another form the invention resides a mobile accommodation unit comprising: a base and a top; 15 the top being able to be moved telescopically with respect to the base between an open position and a closed position; and a lifting mechanism for moving the top with respect to the base between an open position and a closed position the lifting mechanism including: 20 a rotatably mounted shaft; at least one drum mounted on said rotatably mounted shaft; at least one continuous cable loop being wrapped around said drum, the cable loop being attached to said top; and 25 cable pulleys to define a pathway for said cable loop to follow. In another form, the invention resides in a lifting mechanism for a mobile accommodation unit, the lifting mechanism including: a rotatably mounted shaft; 30 at least one drum mounted on said rotatably mounted shaft; at least one continuous cable loop being wrapped around said drum, the cable loop being attached to a top; and WO 2007/104072 PCT/AU2006/001415 3 cable pulleys to define a pathway for said cable loop to follow. In another form, the invention resides in a mobile accommodation unit, the lifting mechanism including: a base and a top; 5 the top being able to be moved telescopically with respect to the base between an open position and a closed position; and a lifting mechanism for moving the top with respect to the base between an open position and a closed position the lifting mechanism including: 10 a reciprocally mounted carriage a drive unit to reciprocate said reciprocally mounted carriage; at least one cable attached to said carriage and to a top; cable pulleys to define a pathway for said cable to follow 15 between said top and said carriage wherein movement of said carriage causes movement of said top. In another form, the invention resides in a alternate lifting mechanism for a mobile accommodation unit, the lifting mechanism 20 including: a reciprocally mounted carriage a drive unit to reciprocate said reciprocally mounted carriage; at least one cable attached to said carriage and to a top; cable pulleys to define a pathway for said cable to follow 25 between said top and said carriage wherein movement of said carriage causes movement of said top. In another form, the invention resides in a mobile accommodation unit including: 30 a bed support for location of a bed; said bed support being movable between an extended position in which the bed support extends outwardly from the mobile accommodation WO 2007/104072 PCT/AU2006/001415 4 unit and a retracted position in which the bed support is located substantially within the mobile accommodation unit; and a removable table located within the bed support; wherein the removable table is able to be moved between an 5 use position in which the table is extended from the bed support and a storage position in which the table is retracted within the bed support. In another form the invention resides in an extendable bed assembly for a mobile accommodation unit, the extendable bed assembly including: 10 a bed support for location of a bed; said bed support being movable between an extended position in which the bed support extends outwardly from the mobile accommodation unit and a retracted position in which the bed support is located substantially within the mobile accommodation unit; and 15 a removable table located within the bed support; wherein the removable table is able to be moved between an use position in which the table is extended from the bed support and a storage position in which the table is retracted within the bed support. Preferably the bed support includes a storage unit that is 20 accessible external of the mobile accommodation unit. In another form, the invention resides in a mobile accommodation unit having a water system, the water system comprising: a first water pump; a water tank fluidly connected to said first water pump; 25 an external inlet fluidly connected to said first water pump; a first water pump valve located between said first water pump and said water tank; and a second water pump valve located between said first water pump and said external inlet. 30 BRIEF DESCRIPTION OF THE DRAWERINGS An embodiment of the invention will be described with the reference to the accompany drawings in which: WO 2007/104072 PCT/AU2006/001415 5 FIG.1 is a side view of a caravan in a open position according to an embodiment of the invention; FIG. 2 is a side view of a caravan in an closed position according to FIG. 1; 5 FIG. 3 is an end view of a lifting mechanism according to an embodiment of the invention; FIG. 4 is a plan view of a lifting mechanism according to an FIG. 3; FIG. 5 is a plan view of the inside of the caravan of FIG. 1. 10 FIG. 6 is a schematic view of a hot and cold water system of the caravan of FIG. 1; FIG. 7 is a perspective view of a open bed assembly according to an embodiment of the invention; FIG. 8 is a further perspective view of a closed bed assembly 15 according to FIG. 7; FIG. 9 is an end view of the open bed assembly of FIG.7; FIG . 10 is an end view of the closed bed assembly of FIG.8; FIG. 11 is an end view of a partially closed bed assembly; FIG. 12 is a perspective view of a partially completed bed 20 support; FIG. 13 is an end sectional view of the bed assembly of FIG.7; FIG. 14 is a end view of a table located on a table runner. FIG. 15 is a side view of a caravan in a closed position; FIG. 16 is an end sectional view of a caravan in a closed 25 position; FIG. 17 is a side view of a caravan in a partially open position position; FIG. 18 is an end sectional view of a caravan in a partially open position; 30 FIG. 19 is a side view of a caravan in a open position; FIG. 20 is an end sectional view of a caravan in an open position; WO 2007/104072 PCT/AU2006/001415 6 FIG. 21 is a side view of a caravan in a open position with a bed assembly partially extended. FIG. 22 shows a top view of a lifting mechanism according to a second embodiment of the invention; 5 FIG. 23 shows a perspective view of a lifting mechanism according to FIG. 22; FIG. 24 shows a top view of a lifting mechanism according to FIG. 22; FIG. 25 shows a perspective view of a carriage according to an 10 embodiment of the invention; FIG. 26 shows an end view of the carriage of FIG 25; FIG. 27 shows a side view of the carriage of FIG 25; and FIG. 28 shows a detail view of the carriage, track, lifting cables and driving cable. 15 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. I and 2 shows a perspective view of a caravan 10 according to an embodiment of the invention. The caravan 10 has been developed to allow the caravan 10 to be taken off road yet provide modern and spacious conveniences that are normally associated with other larger 20 caravans. The caravan 10 includes a base 20, a top 30 and a bed assembly 100. The base 20 includes a chassis 21 used to mount two wheels 22 via independent stub axles (not shown). A drawbar 23 located at the front of the chassis 21. A hitch 24 is attached to the front of the drawbar 25 23 to enable the caravan 10 to be pulled by a vehicle. An alloy space frame (not shown) is attached to the chassis 21 and enclosed using alloy walls 25. Insulation is located within the alloy walls 25. A floor is located within the alloy space frame. The top 30 is formed from a single piece, reinforced fibreglass 30 body. The top 30 fits over the alloy walls 25 of the base 20 and is movable with respect to base 20. The top 30 can be moved between a closed position shown in FIG. 2, in which the top is lowered onto the base 20 and an WO 2007/104072 PCT/AU2006/001415 7 open position, shown in FIG. 1, in when the top 30 is extended upwardly from the base 20. The top 30 is retracted to the closed position 30 when the caravan 10 is being towed and extended to the open position 30 when the caravan 10 is being used for camping. Guides (not shown) are mounted to 5 the top 30 and the base 20 to guide the movement of the top 30 with respect to the base 20 when it moves between the open and closed position and visa-versa. The top 30 is moved between the open position and the closed positions by a lifting apparatus 40. The lifting apparatus 40, shown in detail in 10 FIG. 3 and FIG. 4, includes a rotatably mounted shaft 41 that is located beneath the floor adjacent the chassis 21. The shaft 41 can be accessed from the rear of the caravan and manually rotated by using a Z-shaped handle 42. Two cable drums 43 are located on the shaft, one cable drum 43 located at each end of the shaft 41. Each cable drum 43 has a continous 15 helical recess 44 that extends the length of the cable drum 43. Four vertical cable posts 45 are located within the alloy walls 25. Post cable pulleys 46 are located on each of the vertical cable posts 45. Under floor cable pulleys 47 are adjacent a bottom of the vertical cable posts 45. Tension cable pulleys 48 are also mounted below the floor. Cable 20 tracks 49 are used to mount the tension cable pulleys 48. The tension cable pulleys 48 are able to be moved with respect to the cable tracks 49. Two endless cable loops 50 are wound around respective cable drums 43 and respective cable pulleys 46, 47, 48 as shown in the FIG 3 and 4. Each cable loop 43 is connected twice to respective sides of the 25 top 30. The tension cable pulleys 48 are able to be moved in order to tension the cable loops 50. Two adjustment cylinders 51 are attached to the shaft. A helical spring 52 is wrapped around each of the cylinders 51. Each of the springs 52 is pretensioned to counteract the weight of the top 30. The 30 pretensioning of the springs 52 assists a person to rotate the shaft 41 without using substantial force. In order to extend the top 30 to the open position the shaft 41 is WO 2007/104072 PCT/AU2006/001415 8 wound in a clockwise direction. When the cable loops 50 are wound in a clockwise direction, the cable loops travel up the helical recesses 44 of the cable drums 43. In order to retract the top 30 to the closed position, the shaft is wound in an anticlockwise direction. When the cable loops 50 are 5 wound in an anti-clockwise direction, the cable loops 50 travels down the helical recesses 44 of the cable drums 43. The lifting apparatus ensures that the top 30 moves with respect to the base 20 within the guides in a precise manner. The caravan 10 includes a toilet 60, shower 61, kitchen 62, 10 queen sized bed 63, table 64 and associated seats 65 as shown in FIG. 5. The toilet 60 is located within the shower 61. The toilet 60 is a vacuum, chemical toilet with a foot switch, water flush activation. The shower 61 includes a fully moulded shower enclosure with a hand mountable 3 way valve flip mixer. The kitchen 61 includes a kitchen sink 66 with a flip mixer, 15 several lockable drawers 67, a microwave 68 and a ceramic hot plate 69. A pull out sink 55 and preparation area 56 are located externally. A cold water tap is located adjacent the pull out sink to supply water to the sink 55. A fold down cooking plate 57 is also located outside of the caravan. The cooking plate 57 is powered by LPG gas that is supplied 20 via a portable gas cylinder which is connected to the cooking plate as desired. FIG. 6 shows a schematic drawing of a hot water and cold water system 70 of the caravan. The hot and cold water system 70 includes a first water pump 71 that is able to be used to pump water from three 25 sources namely a first tank 72, town water 73 or alternatively water from a lake, creek, dam or the like water source 74. A first water pump valve 75 is located between the first water tank 72 and the first water pump 71. A second water pump valve 76 is located between the first water tank and an external water inlet 77. The external water inlet 77 includes a pressure 30 reducing valve to reduce the pressure of high pressure water such as town water. In use, a user determines from which water source water 72, WO 2007/104072 PCT/AU2006/001415 9 73, 74 is to be supplied. Accordingly, the user turns one of said first water valves 75 or second water pump valve 76 to a flow position and the other of said first water pump valve 75 or second water pump valve 76 to a non-flow position. The water is then pumped by the first water pump 75 through either 5 a diesel power heater system 90 to heat the water or directly a desired location. The first pump 75 supplies hot and cold water to the shower 61 via a shower three way mixing valve 78, cold water to the toilet 60 and supplies hot water to the kitchen sink 66 via a kitchen three way mixing valve 79. A second water pump 80 supplies water solely from a second 10 water tank 81. The second water pump supplies water to a pull out sink 81 located outside of the caravan via a sink tap 82 and supplies cold water to the kitchen sink 66 via the three way kitchen valve 79. Water is heated within the caravan using diesel powered heater system 90. The diesel powered heater system 90 includes a diesel powered 15 heater 91, a calorifier 92, a glycol reservoir 93 and glycol pump 94. In use, glycol is pumped from the glycol reservoir 93 by the glycol pump 94 into the diesel powered heater 91. The diesel powered heater 91 heats the glycol that then moves through the calorifier 92. The calorifier 92 exchanges heat from the glycol to water that is passed through the calorifier 92 to heat the 20 water. The glycol is then transferred back into the glycol reservoir 93 where the whole process is repeated as hot water is desired. A back up 240V heater element 95 is located within the calorifier 92 and used instead of the diesel powered heater 91 if mains power is available. A thermostat 96 is attached to the calorifier to provide feed back 25 to the diesel powered heater 91. The diesel powered heater 91 is vented externally of the caravan 90. The bed 65 is mounted on a bed assembly 100 shown in FIG 7 to 12. The bed assembly 100 slides outwardly from the caravan 10. In this embodiment, the bed assembly 100 extends rearwardly. It should be 30 appreciated that the bed assembly 100 may be extend from a side of the caravan 10. The bed assembly 100 includes a bed support 110 and a pair WO 2007/104072 PCT/AU2006/001415 10 of side flaps 120 and an end flap 130. The bed support 110 is formed from a pair of bed side rails 111, and a pair of end plates 112. A plurality of longitudinal and lateral cross members 113 interconnect respective side rails 111 and end plates 113 as shown in more detail in FIG 13. A top platform 5 114 and bottom platform 115 are attached to the cross members 113, bed side rails 111 and end plates. A bottom flap 105 is pivotally attached to the bottom platform 115. Two side boards 116 and an end board 117 extend upwardly from the bed side rails 111 to provide a space where the bed is placed. An end board 117 extends upwardly from an end plate 112. A bed 10 side rail roller 118 is rotatably mounted within each of the bed side rails 111 toward a front end of each of the bed side rails 11. A table slot 119 is located within one of the end plates 112. A pair of table runners 150 are located adjacent respective longitudinal cross members 113. Each table runner include a square tube section 151, an L 15 shaped section 152 and flat section 153. All of the sections are joined together. The L-shaped section 152 is joined to the bottom platform 115. The square tube section is spaced from the bottom platform 115. The table 64 fits within the bed support 110. The table 64 is formed from a table top 161 and two table sides 162. C-shaped sections 20 163 are joined to the underside of the table top 161 and the adjacent table sides 162. The C-shaped sections are located around the flat section 153 and the square tube section 151 of the table runner 150. Hence the table 160 can be the extended or retracted from the bed support 110 through the end plate slot 119. 25 The side flaps 120 are pivotally mounted to respective side boards 116. A gas strut 121 extends between each side flap 120 and the end plate. The gas struts 121 biases the side flap 120 to extend upwardly. A cam follower 122 is mounted to each of the side flaps 120. The cam followers 122 are located at different positions so that the side flaps open 30 and close at different rates. The cam follower follows cams 31 that form part of an inside of the top. A pivotally mounted rear flap 130 is attached the top 30. The WO 2007/104072 PCT/AU2006/001415 11 rear flap 130 is opened in order to pull the bed assembly from the inside of the caravan 10. Caravan mounting rails (not shown) are mounted to the inside of the base 20. A caravan mounting rail roller (not shown) is rotatably mounted within each of the caravan mounting rails towards a rear end of the 5 mounting rail. The caravan mounting rail is the same as the bed side rail 111 except reversed. The bed assembly 100 is reciprocally mounted with respect to the base 20. The bed side rail rollers 118 sit on the caravan side rails whilst the caravan side rail rollers support the bed side rails. This configuration of 10 rollers and rails is similar to that provided in kitchen drawers and is very effective in allowing easily reciprocation of the bed assembly with respect to the base. In use, the bed 65 is made ready for sleeping by first extending the top 20 upwardly using the lifting mechanism as described above and 15 shown in FIG 15 to 20. As the top moves upwardly, the gas struts 121 rotate the side flaps 120 upwardly. The upward movement of the side flaps 120 is dictated by the cam followers 121 contacting the cams 31 located within the top 30. Once the side flaps 120 are fully extended, the rear flap is released and moved upwardly. The bed assembly 100 is then pulled outwardly, as 20 shown in FIG. 21, from the base 20 and the rear flap then forms a rear wall of the bed assembly. The bottom flap is able to be opened and closed to provide storage for items such as poles for an annex that may be attached to the caravan. FIG. 22 to 24 show an alternative embodiment of a lifting 25 mechanism 240. The lifting apparatus 240, includes a C-shaped track 241 that is located beneath the floor adjacent the chassis 21. A reciprocally mounted carriage 260 is mounted within the track 241. The carriage 260, shown in more detail in FIGS. 25 to 27, includes a polymer guide plate 261, a support plate 262, four tension 30 members 263 and a drive pulley 264. Two mounting plates 265 extend outwardly from the guide plate 261 to rotatably mount the drive pulley 263. Each tension member 263 has a cable tie point 265 located at respective WO 2007/104072 PCT/AU2006/001415 12 ends of the tension members 263. The four tension members 263 extend through the guide plate 261 and the support plate 262. Holding nuts 266 allow and restrict movement of the tension members 263 with respect to the guide plate 261 and the support plate 262. 5 Four vertical cable posts 245 are located within the alloy walls 25. Post cable pulleys 246 are located on each of the vertical cable posts 245. Under floor cable pulleys 247 are adjacent a bottom of the vertical cable posts 245. Direction cable pulleys 248 are located adjacent the top and bottom of the track 241. Track pulleys 249 are located adjacent the 10 middle of the track 241. Four individual lifting cables 251, 252, 253 and 254 are connected to top at different locations. Each of the lifting cables 251, 252, 253 and 254 extend from their respective connection to the top over respective post cable pulleys 245, through respective direction pulleys 248, 15 through respective track pulleys 249 and are tied to respective cable tie points 265 on respective tension members 263 as shown in FIG. 28. A drive unit in the form of a winch 270 is located at the end of the track 241. The winch 241 is connected to a drive cable 250 that loops around the drive pulley 263 and is connected to a rear beam 271 of the 20 caravan 10. In order to extend the top 30 to the open position, the winch 270 in a clockwise direction. This causes the drive cable 250 to be wound onto the winch 241 and the carriage 260 to be pulled along the track 241 toward the winch 241 via the drive pulley 263. This in turn causes the 25 respective lifting cables 251, 252, 253 and 254 to be pulled toward the winch 241. This causes the lifting cables 251, 252, 253 and 254 to lift the top 30 upwardly. To lower the top 30, the winch 270 is released to reverse the operation. Tensioning of the lifting cables 251, 252, 253 or 254 can be 30 achieved by moving the holding nuts 266 to release the tension members 265. The tension members 265 are then moved to tension the lifting cables 251, 252, 253 or 254 and the holding nuts 266 retightened to hold the WO 2007/104072 PCT/AU2006/001415 13 tension members 265. The caravan described above provides many advantages. When in a closed position, the caravan is similar in height to a standard four wheel drive vehicle. This enables easy, fuel efficient towing of the caravan. 5 Further, the length and weight of the caravan allows the caravan to be taken off-road. Even though the caravan can be taken off-road, the caravan provides many features that such as a toilet, shower and queen sized bed that not normally available in off-road caravans. Still further, the hot water heating system allows the caravan to 10 be able to be entirely sealed if desired as the diesel heater is vented externally. Hence, the caravan is dust proofed when travelling along dirt roads. Further, the caravan can be sealed in cold weather to keep the heat within the caravan and keep the cold air out of the caravan. It should be appreciated that various other changes and 15 modifications may be made to the embodiment described without departing from the spirit or scope of the invention.