The dirty looking area may be from having something rubbing against the surface, though it doesn't look quite like a rubbed area typically does. Usually there is a curved pattern it the discolored area due to having something like a branch or a tarp brushing back and forth against the surface.
You said you don't want the really shiny look. In my experience, which is quite limited, if you only polish it to a low sheen you will have swirl marks that will re-appear as the surface oxidizes. I have seen an Airstream that was just compounded, not polished, and it had a lot of that funhouse mirror effect going on. I have heard of an acid process that might be a better way to approach yours. It apparently doesn't give you as shiny a surface as polishing does, but it doesn't need quite the several hundred hours of labor, as polishing does. I'll try to find info on it for you.
Rich the viking
Originally Posted by Foundtruth
We tried AIRPLANE striper on the blue stripe and the Number Stickers above the Clearance lights. It removed most but it did damage the plastics...luckily we were going to be changing all the lights!. We applied Smart Strip on the body and left it overnight. It removed most except a few areas a second coat took care of the rest. Our 27ft we used 3 buckets at about $60 each. The SmartStip didn't seem harsh on skin, My 5 year old helped apply it also. Then in the morning we power washed it off.
What we have Now seems to be oxidation or something but it doesn't seem to be the clearcoat. On the other side of the trailer it is perfect. This photo is before the second coat was applied to the roof.
We don't want to Polish it to a Mirror finish....