That board was in the boat, I'm guessing from the factory. Most boats have the amps mounted there now. It's 1/2" hdpe. If I were going to install it, I wouldn't bother carpeting it, just more stuff to hold water, and makes it harder to cool the amps. Epoxy doesn't stick to hdpe very well, so you could epoxy a couple pieces of marine ply to the fiberglass hull, and screw the hdpe to that.