When I restored my Starcraft, I screwed the aluminum siding and repair panels in from the exterior, the same way Starcraft did it but used more and better screws. I knew an exterior paint job would be following. If he's not planning on painting the exterior, screw heads can be painted using a Q-tip and paint.
I'm a carpenter, too. There is nothing that unusual about an RV frame other than the wall sections are attached on top of the flooring. Mine was carpeted and the walls were attached om top of the carpet. Nearly all of that was fixed when I repaired the frame. On mine, the floor and all of the topsides are held down to the frame with a few stove bolts through floor and steel frame.
If you are repairing floor sections, the walls can be detached in those areas by cutting staples and screws that hold the wall down to the floor. The new floor sheet is then slid back under the wall. It is tedious but you'll get through it.
Best of luck on the repairs. You're a good BIL.
