Rust proofing door seams

Just curious what you guys do to rust proof your door seams. I have a door that was rust free until it sat outside full of water for 6 months. I cleaned it out but there is some surface rust inside. The seam looks fine from the outside. I think I will pour some POR15 in there and move the door around to get it to the seams.

Would it be a good idea to use the POR15 Metal Prep first? It needs to be rinsed and I am not crazy about getting water in there again.

Any other ideas?