They are all about the same. Since there are a mess of them out there now, do some shopping and don't just snap up the first one you come across...unless it is a smokin' deal! Look at them carefully. Look at the trailer cords to make sure they aren't cut up, look at the air line (s), the late ones have a "service" and an "emergency" gladhand, to make sure of the same. Look carefully at the tongue/lunette area. 90% of the trailers are bent there, they will jacknife easily and that is where the damage occurs. Make sure the e-brakes work, if they do, at least you'll know that that the shoes and backing plate parts aren't rusted solid. Crawl under it and pull the M/C lid off, see if there is fluid in it. If there is, see if you can pull it with the deuce. Do a few quick stops and see if the drums warm up. If not and the e-brakes work, wheel cyls and M/C's are easy fixes. It's kinda like buying your truck, they need inspections to see what's wrong.
Must have items are, the crank up landing gear and the rear fold down leg. And a title
Alot of the trailers have been overhauled/repaired, so they are somewhat of a hodgepodge of parts.
