Best way to seal a leak on an aluminum bateau?

I have a 14 foot long by 3 foot flat bottom aluminum bateau (boat) i need to seal a few leaks on, i'm pretty sure it's the rivets that are bad, i can resmash them but that wont last long, i'm looking for a solution that will last. (i work at a sheet-metal shop so i can weld or use scrap metal to help seal) any suggestions?