floor was plywood fiberglassed on both sides and attached to hull on both sides. They attached the molded fiberglass cabinets with many, many screws. Over the years water seeped into those holes and the plywood rotted in between the fiberglass layers. When I pulled up the top layer of fiberglass, wood chips were enclosed between the layers. A complete floor replacement is what we did to repair it...off the frame, suspended egg, floor replacement.
I took 4 sheets of 4 x 8 marine grade plywood to a local fiberglass shop where they put three layers of fiberglass on each side. We cut the perimeter, sealed the perimeter with fiberglass resin, then glassed it in top side and bottom side. Now I am very careful when attaching things to the floor. The only "breach" in the fiberglass floor are the screws to hold it onto frame but there is a lot of 3M sealant in the holes, the drain for shower, and where we added wood braces to hold the 30 gallon water tank in place. The shower drain and propane
line was drilled out larger than needed, re-fiberglassed and drilled out a bit smaller so that the complete edges are sealed. The water tank brace has butyl tape underneath it and sealant all around any screws.
I'm a bit paranoid about breaching the fiberglass floor from any angle.