I made this to tow behind my 5er. It makes backing up a breeze. The trailer essentially follows the fifth wheel like it's an extension of the frame. Makes for a wide swing in the back end though. I did a ton of research on these before building one. Mine is the only one (that I've seen) to use airbag suspension on independent caster style assemblies. I made everything from scrap steel that I got at the local recycler for $0.28 a pound minus the pillow blocks and the hubs and spindles for the swivel action. I've got less than $400 into it and she rolls down the road at 75mph with no problems. It's not the prettiest trailer out there, but it's purpose built to do one thing.
For those of you who have never seen one, the frame of the trailer stays straight with whatever is pulling it and the two casters swivel to follow. When you back up, the casters swing around and follow you backwards. It attaches at two points on the tow vehicle. I made it for my RZR which is 1000lbs. With it on there the bags are at 55psi. It's got about 8" of travel.
I made this hitch just for my truck. It now has additional bracing on it so it doesn't twist as much.