I would say borrow or rent a rivet gun. Pull the floor out and replace the worst ones and rehammer the leaky ones. Then flip it over and Glovit the bottom. It's work but as long as you don't pound it in the waves or on the beach it won't leak again for a long time. If you don't want to do that use some sort of etching compound on the seams and 5200 marine caulk. I have done both and there may another solution I don't know of.