Tracker, the "Aircraft" paint stripper (which I get from Wal-Mart) should do the trick without damaging the skin of the trailer. It will, of course, also remove any factory clearcote from the skin. If you need to remove the paint without touching the clearcote, I would carefuly use the rubbing compound that is used to shine up or renovate spray painted surfaces on, for example, motor vehicles. It is available from your local NAPA or similar store.
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."