I hear gluvit is good. I used coat-it on the bottom of my boat and 5200 on inside seams.
Coat-it is some good stuff. Little hard to work with, but comes out great when done. Really seals up good and it is pretty cheap. A quart was $20 at academy sports and it did every seam and rivet on the bottom of my boat.
The 5200 is great on inside. But **** it takes forever to fully cure! The coat-it drys in 24hrs.