I have yet to see a re-painted enclosed trailer that looked good at all up close (not counting the mega buku $$ coach trailers) as compared to the original coating on the aluminum. Keeping in mind that the coating on the original aluminum sheets is some sort of baked on coating and not really a "conventional" paint, as in you can't just scuff it and go, you end up sanding the whole thing and priming and painting. I had one done once on a vending trailer that I picked up for a song, and same deal couldn't take the maroon paint and had to have white. I was never happy with the paint job. That is a LOT of big flat surface area, and generally for the budget job on a trailer, it is real easy to see orange peel, heavy spots etc on those big flat sides. Plus way easier to scratch etc. compared to the factory coated panels.
Unless the trailer is really cheap, or really specialized for your purposes, I'd keep looking. There are a ton of used trailers on the market, go to racingjunk.com and look around.