rods 100 and 102 is significantly less than the rate of rotation of the connecting shaft 36 as best shown in fig5 and 6 the l shape frame member 64 has nuts 126 attached thereto and the l shape frame member 66 has nuts 128 attached thereto the threaded rod 102 threadedly extends through the nuts 126 the threaded rod 100 extends through the nuts 128 the threaded rods 100 and 102 are rotatably journaled in bearings 106 at one end thereof the other end of the threaded rod 100 is connected to the gear box 40 and the other end of the threaded rod 102 is connected to the gear box 42 attached to each nut 126 is an actuator member 131 which is engageable with limit switches 140 and 142 for operation thereof attached to the roof 20 and to the frame member 70 and extending the length of the frame member 70 is a flexible wall member 110 which may be of canvas or any other suitable tent like material the flexible wall member 110 also is attached to sealing strips 114 which are attached to the top portion of the body 18 and extend thereacross adjacent the l shape channel members 59 and 61 pivotally attached to the l shape support members 64 and 66 by means of brackets 146 is a u shape brace member 150 the brace member 150 has a central portion which extends between the frame members 64 and 66 and which is attached.