Reinforcing the floor

This weekend I finally tackled the job of adding a new layer of plywood below the original sub-floor.  This was not an easy task, and I changed my mind many times about whether or not to do the job at all.

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.

The next step was to cut a piece of plywood to fit beneath the rear deck of the trailer, below the dinette. The plan was to slide the plywood into position from inside the trailer.  A few things were in the way, though; the wheels, the mudflaps, and the scissor jacks.  The wheels, I simply took them off.

This shows the amount of gap I allowed for inserting the new plywood floor.

I got impatient with the mudflaps because the screws that held them on were completely corroded and wouldn't unscrew, so I just pulled the mudflaps up and out of the way.  The jacks couldn't be moved, so I cut small notches in the new plywood to avoid them.

A piece of 3/4" pressure-treated plywood, cut for the rear deck area.

 The new plywood was cut so that the leading edge (at the step-down from the dinette to the main floor) was exactly flush with the original floor.  The wheel-well edges were flush along the sides but extended to the rear about 3 inches to allow for the bump where the mud-flaps were fastened.  On my Boler, this part is coated in fiberglass.  The curved back edge was cut so that the new plywood comes to about 2 inches from the fiberglass wall/skirt on the underside.  I figured this set-back was still close enough to the wall edge to transfer stresses and loads effectively between the walls and the frame.  I used construction adhesive and wood screws to fasten and bond the new plywood to the old.

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.