I have this same setup...My buddy made it for me.
Its a chain link Welded to the side of the trailer, Attached to a "garage spring"
From the spring is a cable that goes through a series of pulleys then hooks to the gate. Its all covered up by Painted PVC. I think hee used HD AtV winch cable...MUST be HD or you're asking for problems. looks like the real deal! Its really only because he reenforced this trailer so it could handle a mini skid steer
So the gate is heavier because it has ramps for a skid built in.
Sorry for posting so many pictures just thought it would be a little helpful....
For sale too!