Originally Posted by pgandw
Although I'm late to this thread, from my sailboat experience -
Foam core with fiberglass skins is a proven method of building a fairly strong structure (much stronger than the fiberglass or foam by itself) at a light weight. The glue bond between foam and fiberglass is critical to the composite structure's strength, which is why a vacuum is pulled during the gluing operation (as others have said).
The strongest attachment methods are
a) through-bolting with good-sized backing plates on both sides to spread the compression load over the thin fiberglass skin. Bolt holes should be caulked/sealed to prevent water intrusion into the foam and/or glue joint.
b) removing gel-coat, and expoxy glueing on a wood (or metal) mount plate to which the accessory is screwed.
Neither method lends itself to being reversed very well - although it is easier to fill empty bolt holes than remove a mounting plate.
just my experiences
Thanks for the info. Do you see any issues screwing things (molly screws, etccc) into the thin inside wall of the RV to install a shelf. I can't see how this could possibly do damage to the structual intergrety of the wall? (assuming you don't drill all the way thru to the outside, ha)