I bought the Lance plug directly from lance this summer. My truck didn't have the camper package, but I was able to order the GM wiring harness from Amazon. I used all the wires except the ground and 12v. I located the plug towards the front of the bed, as the plug length on the camper end is a little short. I ran a separate circuit from the engine bay with 8 gauge wire and an battery isolater to charge and power the camper.
On a side note. Lance was very helpful, fair priced and fast shipping. I would recommend buying from them.