I've been working on the sub-floor and removed the tie-downs, insulated the wheel wells, created plywood templates and cut & glued the strips of Poly-Iso to the floor. Now I filled in the voids between the insulation panels with a spray foam application.
Although it is a closed-cell, waterproof foam, after cutting off the excess, what remains is susceptible to moisture, but still adds insulation and some structural cohesion to the floor.
The mod can be viewed here:
Mod: Insulated Floor – Spray Foam Application
Van Williams