I just got a new bumper for my truck (yea!) to fix the bent-*** one. I took the old one off and the entire back of it is covered with rust. Thankfully it didn't show around the edges to the outside though.

I don't want the new one to have the same terrible fate. The thought of spraying it with one of those rubberized-undercoat aerosols went through my head. Does that stuff a) actually stop rust, or does it just rust under it, and b) think it'll do any good on the non-visible parts of my bumper?

Thanks in advance all

 

I've used that stuff on a boat trailer and it actually puts a pretty good coat on it, similar to the texture of bedliner. I'm almost certain that water wont penetrate it. Check out the label on the can, it should say waterproof.