I replaced the rear roof vent in my Boler
17 a couple of months ago. While doing that the layers I saw starting at the top/outside:
- fiberglass/resin mixture
- ensolite inner liner (neoprene-like rubber with white vinyl coating)
The roof, sides and bottom all seem to consist of the same single layer fiberglass shell. Ensolite lines the ceiling and walls.
My roof sags somewhat. At some point, I will attempt to counteract the sagging by first propping up the roof into the desired shape, then grinding off some of the gelcoat, then adding several layers of fiberglass and resin.