James,
I couldnt agree more with Phils comments via Randy,, I think that was in Model Aviation a couple months back. I have polished a few (hundred) cars with Urethane on them. Phil's article laid to rest some concerns I had about buffing on models. One comment, I dont remember if it was in the article, but your BEST optimal time to rub-a dub on that clear is usually between 24 hrs and 48 hours after shooting the clear. That is assuming 70 degrees, 50% humidity. Lots of patience and clean microfibre polishing clothes to wipe and inspect.