Mmmmmm...i dunno, I think you guys are over think'n it...
All ya need to do is...
Reach on up there with some sand paper or a sanding block/sponge dealio, brush on some rust converter or primer, brush on some bed liner or undercoating/rust bullet...DONE!
It don't have ta look purdy, we're not tAk'n it to the fair...![]()