I'd suggest: Spray the roof or apply with a rag/brush, Jasco Prepaint Conditioner. Let sit for an hour or two. Spray again and brush off any soil. Rinse and make sure that you rinse the trailer walls (in fact, you can apply the Conditioner to everything, it will remove all the oxidation and grime). Apply a top coating to the roof that is compliant with the roof material (typically, EPDM but you want to know, for sure). Wax and polish the walls with a quality marine or aviation wax.
Light dirt, mildew, or tree debris typically doesn't affect the life of an EPDM roof. It can sometimes shield the material from UV, the major aging component of rubber roofs.