On the seat question, you can coat them with Polyuethene, glass or epoxie resin. If you cannot get a fastener to hold in the floor, chances are your floor may be soft, like rotten, as it's very common in our older boats. The floors are generally plywood, covered with a layer of glass mat, then carpeted. So don't expect an eigth inch of fiberglass to hold your seat in place. The floors absorb water from rain, heavy usage, leaks, water over the side or transom. The plywood floor is not coated on the bottom side, there for it absorbs moisture, and taking on lots of water weight, all while slowly decomposing, and rotting. You may want to check that floor out, before the season hits.
Sleek