The roof of my 34 year old van is developing rust spots. They always start bubbling up under the paint. The underside of the roof is covered with sprayed on urethane foam insulation.
The first two I sanded down. One had a deep pit that almost penetrated the metal. I thought I removed all the rust and sprayed them with Rustoleum Rust Reformer. Then the next day I sprayed them with Eastwood Rust Encapsolater. Now 4 months later there is rust bubbling up under and around the Encapsolater.
I didn’t put any primer or paint over it. I might repaint the van but am undecided and I didn’t want to use the wrong primer. Today I found a new rust bubble coming up under the paint. What is causing this and how do I fix it permanently?