Kip, the 1/2 tons have the same situation. I was told that that cross member is just for additional support for heavy loads. The cross member just bolts to the bottom of the bed boards and when you get a heavy load in the back the bed bows down to where this cross member contacts the frame.

On my truck there were actually wear marks on the frame where this cross member was rubbing. So just bolt it up to the boards and let it go.

Hope this helps.
George