Re: leaky rivets
Get a Sharpy and 2 saw horses.
Put the boat on the horses and get some water in it(2''-3'') and start marking rivets, leaving the leaks and just covering them up works for a while but your boat still leaks and it is harder to repair once you have a thick coating of whatever on it, it is a band-aid fix.
Find the leaking rivets and rebuck them, that requires 2 hammers, one inside one out, then your boat no longer leaks and is repaired correctly and you never have to worry about when your sealer is going to fail.
If you are okay with the band-aid approach you want a product called Gluvit, but again I think it would take less time and no money to fix it correctly.