I know that LBH has the bottom of his Jon coated in Herculiner. My question is, does anyone think it will prevent a tin boat from leaking?

Here's the scenario. My father has an old Jon that has suffered from blown out rivets over the years. I was thinking of replacing the rivets and coating the bottom of the boat with Herculiner or some equivalent to prevent future leaks. It's gotta be worth a shot, the Herculiner is mostly rubber, so it should keep the water out

Any ideas?

Should work just fine.  I would however paint it on the inside not the outside of the hull.  Now I know your jon boat won't be setting any speed records but you really should try to keep the bottom of the boat as smooth as possible.  Plus the liner will give you a nice cusion and sound absorber on the floor of the boat.

good luck,

TD