I'm guessing you do have a D/A Polisher?
I'd first try something as simple, and inexpensive as Meguiars Cleaner Wax in the Red Bottle, gotten almost anywhere.
Having a cargo trailer myself, I know how easily those Clutch Head Screws will tear the living daylights out of Pads, so best to stay away from them as much as possible, and finish out in those areas by hand with a few MF Applicators.
One can simply repeat the process if needed, then follow with a more durable product, Collinite #845 would be a good choice.
One product I have found that strangely does not at all work good with the paints on these Trailers, is any of the Duragloss products such as #501, or #105. I know, I've tried them and found they are then impossible to remove.