Do you want to seal the entire hull ? or patch leaking rivets and welds?
Lots of choices to seal the entire hull. check out topic https://forum.tinboats.net/viewtopic.php?f=3&t=11977
For leaks, you will have about 100% feedback on the 3M-5200.
The regular 5200 is a little on the runny side, does not hold its shape like silicone.
but will flow into cracks and crevices with gravity (somewhat)
there are TWO types of 5200.
Regular - takes SEVEN days to fully cure. (yeah, one week)
Fast Cure - takes 24 hours to fully cure.
It is also an excellent waterproof adhesive.
I could not find the fast cure and grabbed a tube of the regular and sorry I did not
take the time to go to another store ..... the regular 5200 slow cure is messy to work with.
comes in the toothpaste tube size and also a caulking tube if you have a lot to seal up.
A little bit goes a long way.
Be prepared to pony up about 10-$15 for a 3oz tube.