I've heard of the POR product and may eventually try it. I had similar rust along some of my exterior compartment doors. I removed the seal, sand-blasted the areas, and used Rustoleum's new product, Rust Reformer, followed by flat black paint. So far, all looks well.
In some other areas, I've used Loctite's Extend rust-converting product and I'll be interested to see if either of these products hold.
'07 Country Coach Allure 470 Siskiyou Summit #31578, Cummins ISL 425; 2014 Ford F150 toad; Air Force One Toad Brake.
Glen Allen, VA; Smith Mountain Lake, VA.