I have that same trailer. I also had close to the same rust issue, only my fenders had big patches of rust. 7-8 years ago I disassembled side steps and fenders. Wire brushed, then used spray on rustoleum rust converter,(only in rusty areas) sanded then a second coat. Next I sprayed 2 coats of brown rusty metal primer and followed that up with rusto semi gloss white reduced and applied in 5 or 6 coats with a foam roller. Wet sanded between the last few coats. I only rolled on as I had the boat on trailer. The remainder of the trailer just got a light scuffing with rusto directly rolled over top. I even used JB as a filler on the outer side of the step frame for filling deep pits. lol:lol: Even though the boat was covered, the trailer sat outside for 4 of those years and it still looks good. I,m just now seeing a little rust color next to the carpeted step and that's probably for not prepping the tray the wood lays in.. Judging by looking at your close-up frame shot, that trailer has plenty of meat left. That's steel, not the white stuff. Hope you get her figured out Watermann.
I enjoy your build threads and look forward to seeing you bust out another Starcraft, nice work.