HI
Just a quick postto bring this up to date. I used CRC low expantion foam. In mu opinion none of the regular foams sold in the home building stores will do. It is denser and does not tend to tear things apart like the regular foams. I installed blocks of wood wherever screws would have to go in and secured them from at least one side with an adhesive. Before injecting the foam I made a dry run with clamps and boards to make sire that I could get the clamps on fast. I ised hardwood 1x8's and clamped both sides. I shot the foam from any gap I could and in one place I had to drill holes whinh I will fair over later. The foal that camo out around wheel wells can be fut with a seaated bread knofe. The expansion makes the old wavy outer sheet nice and flat and the result is solid. I will come back with pictures and more info later but this has worked well. Still solid 3000mi later.
