Those 2 part epoxy primers seal nicely. I took my truck to bare metal and was priming and doing body work, but I ran out of money. The epoxy is holding up very well to moisture. The places I used etching primer to cover bondo when I'm not done filling, but need to drive rusts through in about a week or two and a have to sand it all off. Only prob with the epoxy is it loads up your paper if you try to sand it, unlike the etcher.