My experience isn't quite applicable to your situation - but, since no one else has shown up, I'll share it.
I have a 2004 Rockwood Roo 25BH - and I have done quite a bit of work on the floor (the previous owner let it sit - water got in through the hybrid bed door and other places). My floor is framed with 1.5" square aluminum tubing, 16" on center for the floor, with foam insulation between the aluminum frame tubes, then layered with thin plywood on both the top and bottom of the frame. The floor additionally has a heavy layer of black plastic tarp-like material on the bottom (sadly, this layer is so watertight that it held water in the floor, contributing to rot). It looks like they used some kind of vacuum press to glue the whole sandwich together. It's basically a good approach - as long as everything stays dry. The dry portions of my floor are in good shape.
From what I have seen during my rehab project, the walls and roof of my Roo appear to be framed using the same basic structure - except the walls and roof have different outer and inner layer finish materials.
I recently found a soft spot in my roof, so I'll find out more about my roof structure at some point.
If you're interested, I can supply some pictures of what my floor structure looks like after removing lots of wet rotten plywood. Send me a private message!
Phil
'04 Rockwood Roo 25BH
'05 Chevrolet Suburban 2500
