I'll put my vote in for Rust Bullet. I have used both POR 15 and Rust Bullet. Here at the beach the Rust Bullet seems to hold up a little better. Only problem is that you need to use 2 coats. A base coat and then a re-coat in a few hours or the next day to fill all the microscopic pores from the first coat. The silver rust bullet is some crazy nasty stuff. When you open the can and stir it.... It looks like it is alive!
I used in in the hinge pockets and inside the door bottoms to prevent any rust from ever happening there. A good preventative measure.