I just spent the last week doing mine. 2005 22ft Cruiser. 2005 Pacific Trailer. Galvanized. Took the old rusted bunk risers off and ordered new ones. I ground down all rusty parts of the trailer with wire brush bit on my grinder. Took some time and made a royal mess. After getting it all cleaned I treated all areas to be painted with Ospho, let stand for 30 minutes and washed off as per the instructions on the Ospho bottle. Once dry, I painted areas with a few coats of a cold galvanize spray paint.
I did not spray the entire trailer, just key elements (axles, fenders) that had rust damage. I won't know how it holds up for a while, but I'm happy with the results, and the trailer went from looking embarrassing, to looking pretty good. I feel better about the structural integrity of the trailer having removed the surface. The trailer should have years of life ahead of it.
And yes, I took the time to re-wire the trailer (including changing all grounding hardware and waterproofing all wiring connections), as well as change out the bearings and get work done to the brakes...