You may wish to shop around for body shops in your area that would take on this job. Since the trailer will be new, there won't be extensive prep work to fix surface irregularities.
FWIW, I painted my trailer with an airless sprayer. It is aluminum sided. The paint is pretty much just like the day I painted it, six years ago. I didn't have any decals, just accent stripes. If you wish to have an automotive style paint job, the pros use HVLP guns and will get it right.