Hmmm...I'm curious what's under the paint, bondo?
The problem you may have, is anything that would remove the paint will also remove the clearcoat, if it hasn't been stripped &/or polished earlier. That's no biggie if you are prepared to strip the entire trailer in preparation for polishing, but otherwise you will remove the paint & clear coat leaving the newly exposed aluminum to oxidize at a different rate than the area with clearcoat remaining. Over a couple of years (or quicker depending on your climate) it'll darken where the clearcoat was removed.
That being said, there are lots of different opinions on stripping & products to do so, I have found Kleen Strip's Aircraft Stripper (available @ WalMart, Pep Boys, Auto Zone, etc) to work very well. You can perform a search using the keywords "stripping clearcoat" and get lots of info on different products others have used.
If you use the Aircraft Stripper, be sure to wear gloves & follow all label instructions & warnings...it's nasty stuff!