We stripped off our clear coat with aircraft stripper. It was failing in many areas. Some swear by the environmentally friendly strippers, but it didn't have any effect on ours. Once the clear coat was off, the trailer looked much better overall, to the point we've been asked how we've polished (we haven't yet). We are still exploring what we want to use to get the mill finish we're going for. We use car wash and wax, cleans the trailer well.
Polishing is kind of a religious subject here on the forums. There are many threads devoted to it. Some of it seems to depend on what you want your final look to be. We don't want high polish because we don't want to spend the time to maintain it. That said, polished trailers are BEAUTIFUL!
Keep reading, and welcome!