Rust proofing door seams

I have done this for decades: pull the door anel, clean out all the debris hose it all out till it drains clean out the drain slots in bottom of door, reach in and try to remove any surface rust with paper, scotch pad etc. ,spray it good with Ospho, let it sit all day, next day do same again with Ospho and then NEUTRALIZE IT with water. Then I will coat the insidie of door with epoxy primer and a pr9nter brush, then I tp coat with heavy enamel like Rustoleum out of a can NOT spray can. I quit using Por 15 3 decades ago, too expensive and other stuff works just as good for me.
I do th same on bottom inside edge of door basically, except it will get topcoated with auto paint, if needed paintable auto seam sealer.