I just used rust oleum gloss black in an aerosol can. Remove everything attached to the frame, mask off anything that can't be removed, scuff it real good, use a wax and grease remover solvent and spray away. I would also mask off the lower 3-4 feet of the trailer front and rear to keep the overspray off the front and rear of the trailer. I also removed my stabilizer jacks and separated them separately. In the end it will look as good as new, maybe even better!
I did mine last year. Between waxing it and painting the frame it looks like a new trailer!