Wow - that's quite a project. My roof had some moisture so I drilled out some 1 inch holes from the ceiling but not penetrating the top layer of fiberglass. I found a mix of plywood - mostly the rear section, and balsa core. There's a separate fiberglass headliner about 1/8 inch below the structural roof. When you're in the cabin looking up at the white ceiling that's the fiberglass liner.
|