I've never used the POR15, but did by some floorpans that were coated with it. As stated earlier when I scrapped it off there was rust below it. When I did my frame, I cleaned all the old material off, scuffed it up, used self etching primer then Sherwinn Williams commercial chasis coat with hardner. It's pretty damn durable and easy enough to touch up as needed. As with any coating it's all in the prep.
