Sorry, meant the frame. POR is great for the underside of the car, specially if you have t-tops and some leaks. The fiber repair kit can save some headaches on small holes. I used POR from the firewall all the way to the back bumper. Had to clean down to bare metal and let some surface rust form for it to stick good. I even used their filler in a tube to caulk in all the seams and joints.
I used the black gloss POR on my frame and I'm not sure I like it as much as I thought. For the time and hassle I think powdercoating is gonna be the way to go. About $400 for the frame (no missed spots. no more surface rust either)