I have done a couple of trailers over. I also work on classic cars on the side. I have the equipment to sandblast / prep / paint anything from trailers to small parts to show cars.
You DO NOT have the equipment to sandblast it. You will kill that compressor!
If I were you, I would:
1. pressure wash
2. clean with prep solvent, lacquer thinner, or mineral spirits
3. DA as best you can with 180 or 220 (60 is way too course)
4. Use a course wire brush in a drill where DA won't fit
5. repeat 2 (I like lacquer thinner best). Use a WET rag followed immediately by dry.
6. prime
7. paint
I am a big fan of Rustoleum, sticks well, inexpensive, somewhat durable, AND EASY to TOUCH UP. You could use rusty metal primer and satin black paint (gloss will show more of the imperfections and sand lines). It could be brushed, sprayed with airless sprayer, thinned and sprayed with cheap automotive spray gun, or rattle canned. All have advantages and disadvantages.
You could also buy some Epoxy primer and the mixers, an automotive spray gun (your compressor will work hard, but should do it, (use disposable water filter at gun). Then use a decent Urethane paint or the paint mentioned above.
my .02
"on the cheap" I would use Rustoleum all the way....