Hi, I recently repainted my smaller 2 horse trailer and, it was fun, and not as expensive as one would think.
For the base coat, I went to the farm store and bought gray tractor primer, $30.00 per can, it took 2 cans and 2 coats, I lightly sanded between each coats. Then, I went to O'Reiles Part Store and bought car paint. It was an all in one stuff, paint and topcoat, they told me its very sturdy and will give rather than crack. 1 can of that stuff worked well, you sapposed to add mineral spirits and something else. I think I spent $130.00 at O'Reilies. Bought mineral spirits at Wal-mart, cheapest place for it and it worked well. I sprayed it on, it took 2 coats, sanded lightly in between. Someone could easily put a 3rd coat on for the "deaper" look.
I traided it off for a larger trailer and the guy likes my paint job, he uses the trailer to haul his daughter to the trails and back and down gravel. So far its holding up.