I actually applied before polishing, because I had a lot of leaks. If you can, do it after you polish, because the polishing process messes up the Tempro (turns it black) and you have to go back & clean it all up again (lacquer thinner or mineral spirits will take it off). I didn't clear coat my trailers. The clear coat Airstream uses is different that the clear coat you can purchase at an auto store. It has some kind of plastic in it, so it has some give while traveling. I just put on two coats of caranuba wax right after I'm finished polishing & wax it again in the fall. I actually put a cover on my Sovereign
(gasp!) and just took it off to show it to a potential buyer. It looks fabulous & I will cover it again if they don't take her home. I used a lot of rope around it both long ways & around to keep it from blowing. Since there's no clear coat, the only thing that could scratch is the aluminum. I figured I could buff out any scratches that might appear, but there weren't any!