just put one together for a buddy. his wife got him a foldable one for christmas. Not too bad for what they are and what he's going to do with it. (tow w/ a car around town) They bolt together and are pretty lightweight. 1500 lb max and not over 45-50 mph.
Weld it together, put a beefier axle under it and it would be a 1/2 way decent trailer.