Marine Plywood is my 2nd choice for floor core over foam board. True marine plywood is hard to come by & costs more than the foam board. ( the OEM floor was not marine plywood but A-B grade Fir Plywood, also hard to come by now) There is a fine line between the proper wood preservation, structural lamination and going overboard & overweight. It's easy to go overweight (I'm a good example) and this causes sluggish performance and wakes that get really hard. Resin saturation is needed on top & bottom & edges (I like to reduce the resin for better penetration) Mat fiberglass aka CSM is a filler material and not structual, your floor is a critical part of the hull bottom & needs to tie into the hull system properly. I would apply one laminate of 1.5oz CSm on the bottom side, and a "Fab-Mat" fabric like 1808 to the top side at the floor/hull side joint 5-6" up the side & 5-6" onto the floor, and a 6-8" strip of CSM tying the floor to the stringers in the center section. Then fill the cavities with foam, then cover the floors with (1) 1808 including the hull side 3-4 " with fiber orientation front to back.
If any of these materials are hard to find near you & you want me to make this stuff available on my parts site I can do that if needed.
