Rusty metal, how to prep for paint

Good luck

You need to at least remove the loose/flaking rust. Wire brush the entire surface and then wipe clean with mineral spirits. Go to local commercial paint store (Ameron, Sherwin Williams, International Paint, etc.) and get what's called "surface tolerant epoxy" paint. It'll come in two parts--one the paint itself and the other the catalyst. Spray a couple of coats on per the instructions and you'll have a solid paint job--very hard and tough after curing. Don't expect an enamel type gloss but it'll be a good coating system for "unblasted" steel--although a sand sweep would still be better.

This paint is often used in the steel ship repair business and in paper mills, etc. There are epoxies available that come in one batch, but I haven't used them. This is a "hot" paint and all safety precautions for breathing and eye protection should be followed. You'll also need a good hot thinner for cleanup of the spray rig--the paint seller can provide that too. Not all colors are available, but I've gotten it in white, black or gray, but I'm sure others can be found.

Could I ask why you don't want to sandblast the trailer? If you simply don't want to sandblast I'd suggest a couple of options (both require a little more elbow grease). First off you could go for a small hand grinder with a wire brush wheel. I have no access to a sandblaster so this has been my primary rust remover over the years (which has to be carefully used so as to not damage the metal). Secondly, if you have lots of time you could always go for a rough grit sandpaper and take care of the surface rust that way. Now, this all depends on your reasons for not wanting to use a sandblaster. So, if you could, let us know just why you seek a different method. God bless.

--old fashioned farmer