The ONLY way to 'stop the rusting' , is to remove 100% of the *(*&%#$^& powdercoat 'paint'. probably the worst 'paint' invented. Unless 100% of it is removed(no 'fun' task', water(moisture) migrates under the paint and attacks the steel. A true no win scenario. In 5 decades I've never seen anything powder coated actually NOT rust once it gets a chip, ding,cut, slice. i do like the trailer though ! Thinking of trading my 6x10 tandem for one like yours.
I wondered about a hitch on the chipper but front end of tractor would be a 'tad light' !!
Sounds like you need a galvanized trailer.
N and N trailer out of Canada is a good one.