[carpfisher]

I used a locking mandrel Pop-Rivet simaliar to what was mentioned above. Look at Mcmaster-Carr .com. More kinds of rivets thatn you'll ever need. The other thing I did when replacing rivets was to dip the head of the rivet in Permatex to help with the sealing.
If you have access to an Air Compressor, the Air Driven Pop-Rivet guns really pull those things up tight. A lot better than the best hand powered gun. Tin boats sure are a lot easier to repair!

Greg