I did no foam on my Sunsport and it has worked well. I used all 2x material for stringers and cross braces attached to each other and the hull. I went with epoxy resin from US Composites and also used CPES on all my wood. I agree on the limber holes...put four in my main stringers and every cross brace had the corner cut out. For the structural work I used the DBM 1708 biaxial fabric...for the deck and other areas not needing as much strength it was mat and cloth.