I am re-doing the floor on my boat.?

The floorboards and transom were completely rotted out of my boat when I got it. It’s a 1977 Galaxy 17ft 175hp. Right now I’m putting down pressure treated plywood for the floor, I couldn’t afford the marine grade. But when I have it all down I want to fiberglass over the whole thing to make sure no water ever gets in there again. Are there any sealers out there that are better than glass or is that my best bet. I was toying with the idea of using rhino shin, like in truck beds, but I don’t know how that would work out. But I will have marine grade carpet down over it when its all done so texture and looks won’t matter.