The first step was to lift the body up and off of the frame using a pair of scissor-jacks. Knowing that they would be pushing up against the existing plywood floor, and that this force had to be transferred to the fiberglass walls without fracturing any part of the floor or the walls, I had to be picky about the location of the jacks. This is the part that had me changing my mind about the job -- it wasn't a matter of cost or effort, but technique, because I didn't know how I would suspend the body without interfering with the insertion of the new plywood. I settled on locating the two jacks against the very back wall where it curves below the sub-floor about 3 inches.
|Two scissor jacks located right against the back wall. The frame is held up by a chunk of 6X6.|
|At the front, two axle stands were used to maintain a little left-right balance.|
|This shows the amount of gap I allowed for inserting the new plywood floor.|
|A piece of 3/4" pressure-treated plywood, cut for the rear deck area.|
Next, I cut plywood for the front deck, and for the kitchen cupboard area. I used basically the same approach as the rear deck for lifting up the body, inserting the plywood, and fastening it. The old sub-floor for the main floor area seemed to be in good shape, but it was made of two pieces of plywood, held together by corrugated staples and fiberglass. I cut a single new replacement piece. The net effect is that I gain an extra 3/4 of an inch of headroom, since the body and ceiling are that much higher but the main floor isn't.
The very last thing I did was insert 2" x 2" pieces of new plywood into the gaps where the frame emerges from the bottom edge of the wall. The gaps were because my new decking didn't go right to the very edge of the wall. I figured that much of the load transfer between the wall and the frame happens right at this point. I wanted to ensure that the fiberglass wall met the frame solidly rather than its load getting transferred back through 2 inches of old plywood. I'm just guessing that it matters.