I've a pendle 3 bike wheel support. They come in two styles, one that clamps on the ball, and the one I've got that adds a plate between the the towbar bracket and the ball.
Neither will allow you to tow a trailer at the same time as having the rack mounted. They also do one that will allow towing (crossbars of bikes sits on two prongs a bit like strap-on racks).
Only downer with them is opening the tailgate/bootcan be problematical with bikes fitted, though they now do one that tilts.
Nice people to do business with, my light units failed (after ten years), new set with wiring loom was only fifteen quid.