Anyone ever build a landlock?

I was thinking about doing this rather than spend like 300 bucks. Why not just buy a big peice of polyurethane foam, shape the way you wnat, paint it fiberglass it with poleyester fiberglass and then seal it. It doesnt seem to difficuly and if u scre up on the rails a little it wouldnt really matte ras you arent recieving to force from a huge wave and ur only going 9 mph. Any further thoughs to this would be good.