I live in the northwest so I have had a lot of rain to test the trailer for leaks. I found six small leaks all at a seam or rivet. One on each end cap.
At first I used Vulkem and spread it over the seams. Let it dry and it did not stop the leak and didn't seem to like being spread over the old seam sealer the factory used in 65. It was very easy to peel off. I had read about one of the builders here using the LeakSeal by rust-oleum. This is their version of the stuff you see on TV. You know the screen door boat???
I decided to try it out.
I am very impressed. It sticks like glue and all of my leaks are gone. Its easier to apply than Vulkem. Only bad part is it stinks pretty bad so apply it and let the trailer air out overnight.
Of course I do not know how well it hold up over time? Its flexible so I don't think it should be an issue