I re-painted a trailer of mine using etch primer & a gloss car paint a few years ago. I didn't spray it as I hadn't got the equipment or a suitable place to do it so I used a roller
. The roller I used was one of the small gloss ones & it gave a lovely finish. The coat had very few marks in it & it looked a quality job. I painted the trailer blue with a grey roof & framework & the bottom 60cm of the body also grey & the mudguards black. IT looked really good. I think the paint etc cost me about £70-80 & my time which cost nothing.
I bought the trailer for £500, it was sound but had oxidised drab paint. I used it for 3 years & sold it for £800 to the first person who came to view.