I made a dump cart for my Kubota, but sold the tractor, so I adapted the cart for my Zero-turn mower. I had to weld wheels on it; swivel wheels. I welded two support arms so the cart would be rigid, as the swivel wheels do the turning. The cart stays parallel to the mower, the wheels do all of the turns.
I am adding a support on the top-front of the cart where the angle-iron is.