Are you sure the boat doesn't already have flotation? If I recall correctly, all boats built in the United States after 1965 measuring 16 to 26 feet were required to have full, upright flotation. I could be wrong with this one, but I don't have time to search the Federal regs. You may be able to Google this one and find out. A lot of smaller boats, those ranging 10 to 16 feet, have foam blocks beneath their bench seats, and the boats that are double hulled usually are foam filled between the inner and outer shells.