Back in the early 80's I worked for a place with a high $ powder paint system. I sandblasted my truck's rear step and tow bumper and ran it through. Bumper outlasted 4 trucks and there was still no rust. Not sure how a trailer would do but I assume it would work pretty well.
And my experience is the opposite. Had a custom rear jeep bumper powder coated and it rust badly and was hell to strip again to paint. Yet some of the items I bolted to it a few months later was ospho'ed and painted with rustoleum and was holding up well 6 years later.
The bumper was supposedly sand blasted before being coated, was it? Did the coater use good powder and was the oven the correct temp/time? Don't know but I have seen several powder coated trailers rusty already.
My 38' sundowner frame is sprayed with bedliner and is doing well after 15 years.
2 years ago I wanted a small trailer since I got rid of my pickup. Looked at some powdercoated trailers but noticed that they didn't hold up all that well. I decided on a hot dipped galvanized trailer or aluminum. I ended up purchasing an Aluma trailer (5410 tilt with side kit) in Elk Mound Wisconsin when I was on vacation up there. Been throughly pleased with it.
Another note. Small trailer wiring is typically atrocious and is typically subjected to salt spray do to the use of crappy connectors. Most use 3m scotch locks or insulated crimp connectors. Both allow salt spray to get into the wiring. Dad had over 50 semi trailers and for years I maintained them seeing how poorly these performed.
Better manufactures use bare crimp connectors and slide heat shrink over that has sealant inside. They will also use Trucklite or Grote sealed led lamps opposed to the crappy Hoppy and Chinese small trailer lights. The best will use harnesses with splices covered in molded rubber. Haven't seen that except on semi trailers.