Greeting,
I restored two catamaran trailers this year.On my large trailer(Hobie 21SE),I use paint stripper to remove 3 layers of paint.I could not find a sandblasting outfit with a room large enough to blast it.Stripping that old paint was something that I will never do again,way too much work.Don't make this mistake!
I dismantled each trailer completely,painted each part inside and out and reassembled them with all new grade 8 bolts.On my 21 trailer,I moved the axle forward 24" to reduce the tongue weight.I added some steel and covered the entire trailer with 1/8"aluminum tread plate,added two aluminum tool boxes (that you see in the back of some pickup),built a aluminum frame to hold my 100 qt. cooler and added a 14' round X 10' 2'' long aluminum tube for my sails and rudders.Over the years this trailer grew heavier and heavier so the tongue weight was way too much and moving the axle was a good fix.
I cleaned all tubular steel on the inside and then used Permatex Rust Treatment on the insides of all tubular steel before priming with white.I used a rather expense xylene based primer on the outside followed by it's matching top coat.Way too expensive.I did use bed liner on everything under the trailer before topcoating.
On my 16 trailer,I used Rust-oleum paint with equal or even better results then my 21 trailer.I would only recommend Rust-oleum, It dries fast and looks great.I did change out the tongue tubular steel for a longer piece that added another 18" in the front and ran that new steel all the way back to above the axle(as opposed to just a 24" pass that "Y" part of the trailer) .The trailer was too short and this improved road handling also.My 16 trailer has a custom built aluminum thread plate sailbox that holds two sets of sails and a redwood tray for my rudder assemble.You could dance on top of this sailbox and not damage anything but your reputation...
Bill 404 21SE