There is a handy spot on the bumper just inboard of the driver's side arm. In addition to the breakaway bracket and the Velcro, I attached a (real man's) zip tie around the main receiver for additional holding power.
By the way, I had gone ten years without ever pulling the plunger out of the breakaway switch. I REALLY had to hang from it to get it to separate. Those pesky instructions advise you to pull the plunger periodically, but what do they know?