No experiance of locos, but plenty of similar things. The small trailers available all over with galvanized body and rubber suspesion are pretty good for the price, hard to make one cheaper. A drop-down tailgate is a must to me, makes loading so much easier. Some have very short drawbars , this makes reversing difficult. Put tyre sealer in the wheels and get a spare !.Make a good timber box that can be fastened to the floor. I would clamp the machine down, maybe from its chassis, esp' if it's sprung. Don't forget a good hard cover for the trailer, and a tow hook lock.