I've got an old junk utility trailer that I need to replace for it's job of dump runs and such. Thinking it might have a second career as a manure spreader. I literally found this thing along the side of the road with hand painted sign on some plywood "FREE"! It had a stripped ball hitch clamp bolt that I had to re-thread a size larger, but that was all it took to make it "usable". Trouble is, it is so rickety I'm always a little leery of taking it on the highway. I think it could handle a couple miles an hour around the pasture though. I'd rather put money into a good trailer to go on the highway, in fact I'd like to get something that could haul my JD 790. Maybe something with removable sides.
So it seems like it might be possible to start with an old junk trailer like I've got and add the drive mechanism to scrape the box and discharge the manure. Nearly free is a price that always gets my interest. I am not disparaging these nice shiney new manure spreaders mind you. Just seems like maybe this is an area where I might get by with a lot less.