SanSun, welcome to the Sunline Club. Part of the fun is shining them up to make them look as good as possible
You don't say whether you have Al or fiberglass siding, but either way you'll have fiberglass doors and front window awning. The cure is lots of elbow grease, and, unfortunately, there is a limit to what can be recovered after years of neglect. Nevertheless I still encourage you to give a try.
Sunline promoted their "Krystal Kote" no wax Al siding. However, wax does not hurt it in anyway and any trailer should be waxed. Wax removes black streaks and puts down a slippery surface that deters their return and makes them easy to wipe off with a terry towel when they do come back. Several of us use NuFinish, which I've used on cars for years, but any high quality wax that you like should do a good job on the trailer. Do not wax decals. 303 is a good UV protectant for all decals, vinyl or rubber, including tires.
Read this thread of fiberglass restoration
to get some ideas on how to tackle the doors and window awning.
Wash the roof before doing any waxing of the siding. Virtually all cleaners, except automotive car washing soaps, will remove wax a lot faster than you can put it on. This includes black streak removers which should only be used in a spring clean up before waxing. Do not use any solvents on the rubber roof. Wash it with an all purpose cleaner like Awesome or even laundry detergent like Tide. I wash off of a top quality 8 ft. step ladder--the roof is not walk on--using a stiff bristle brush and telescopic handle. Rinse immediately after washing and rinse the sides too so dirty runoff doesn't dry. Obviously a cool cloudy day is preferred--nothing different than washing and waxing a car.
All of this obviously takes longer than a car and is a lot more work if you have the corrugated Al siding. Depending on stamina, many people divide this kind of major spring clean up over several days. I wash my trailer when it's dirty and wax at least twice--spring and fall. I wash the roof about every other time--depends on where we've been with the birds and tree sap.