One thing is I've heard that POR-15 is amazing for painting OVER rust, but does not actually stick well to other paint or bare metal. I have no first hand experience, just what I've read about it on various forums.
From the picture on Amazon: Note it says designed for "rusted, sandblasted, and seasoned metal" - which backs up my above statement to some extent.

From the picture on Amazon: Note it says designed for "rusted, sandblasted, and seasoned metal" - which backs up my above statement to some extent.
