I called B&W directly to find out what they recommend and why. Their Recommendation is to cut the bed rug to ensure the tightest possible fit between the hitch and the bed/turnover ball frame. The idea is that they don't want any flex points that could allow the bolt you torque to 60lbs to work loose at all. They don't want to risk the pin having any "slack" at all that could allow to beat itself to death in the turnover ball socket.
Cut the bed mat. if you want, keep the pieces and put them in place when you're not running with the hitch installed. For me, that was too much work.