I bought a cheap undercoating kit from JC Whitney and used it to apply POR15 inside the frame using the wands. I also top coated the exterior of the frame with Plum Crazy Purple about 45 minutes after spaying POR 15. You must do this while the POR 15 is tacky. Now the purple is as tough as the POR 15. Great stuff, except for the UV issue.
1985 CJ7 - total customization underway, Sublime green and Plum crazy purple, Ford 9", 258 w/ Holley 475
1985,93 CJ7,YJ - L98 TPI Vette motor, Atlas twin stick, Dana 60s front and rear, Arbs, 39.5 Swampers