My 02 TJ has some light rust on several areas on the frame mainly on some of the welded areas. Inside of frame is smooth, under the skid plate looks good. I want to get rid of these spots and have done a lot of research on POR 15. But I don't feel like the entire frame needs to be painted. Should I use POR15 on these small spots and paint over the frame with regular under coating paint? Any helpful hints would be great.