I had the same thing happen, went to set up an electrical system and discovered the foam was saturated and starting to rot the deck. Pulled it all(what a pain) and replaced it with blueboard. Left lots of drain channels and room for circulation. The challenge seems to be in getting enough material for buoyancy.
The fact of the deck(specifically the screws attaching the deck to the hull) would be supporting the wjhole boat also occurred to me. I suppose there are probably around 60 screws on my boat, all told, attaching decking, and the boat is 600 pounds with gear, that's 10 pounds per screw. It doesn't seem unreasonable if the attachments are sound. This all conjecture, though, and to me the more concerning thing is getting enough square footage of bluboard in there.