Are the sides of the trailer the pre-painted sheet metal riveted to support beams or are they gel coat fiberglass sides?
Gelcoat will be tough, like your rescue unit was to remove ghosting as the faded to "protected from the sun for years" contrast will actually be beneath the outer layer of gel coat. The scratches and or tree drags and other marring can be leveled out of the gelcoat, but a good percentage of the sun fade will remain beneath the outer clear layer of the gel coat.
If the trailer is the pre-painted sheet metal, the paint is likely pretty soft and will buff clean through fairly easy with an aggressive compound and pad. It's best to try something fairly non aggressive like M-205 or perhaps even PB Pro-Polish on a polish pad. If that's not enough, step up to testing a cutting pad with the light polish before jumping to the aggressive end of the scale with a full out compound.
The chemicals in PB Pro-Polish may be enough to reduce the oxidation while keeping the softer paint lubricated during the polishing process.
If you do step up to a heavier compound, first test it out on a soft pad like "Steve-A-Reno's" red VC pad and see how that works before jumping full aggressive with both chemical and pad. Take little baby steps from mild to aggressive until you find that magic bullet that gets it done in one single step, rather that doing multiple steps and wasting valuable time.
Be aware that strong solvents like lacquer thinner can remove that soft paint in a flash!!!
As always Bill, you can call me if you need to or just want to.
