gknott, I would think the easiest method, and one I plan to use, is to attach 1/4 to 3/4 Styrofoam pieces cut out around all visible hardware. I know I'm lucky living were condensation is minimal compared to other areas, but any leads to mildew, and I don't want that. So, I to will take the precautions to insulate to combat the condensation issue.
I will then put up the FRP with mahogany batons running port to starboard, attached with screws to 3/4 plywood attached using polyurethane, using wood buttons to plug the screw holes in the batons.
For the odd shaped sections, above the Galley and 1/4 birth, use crown molding the size large enough to across the protruding portion to intersect to a piece of 1/4 mahogany plywood cut to to shape of the triangular section. If i can't find a crown molding piece, I will cut a of mahogany, ripped on a table saw at the necessary angles needed. Then put some 1/4 round and corner trim mahogany to cover the intersecting locations. I have photo below showing the approximate area in black. The picture is before I removed the headliner.
As I said before, I will post up my project once I have done the modifications.
Good Luck if you do yours first!