Set the camper in the truck on top of the harness. Caused some strange power spikes in the truck, and didn't have tail lights for the better part of 300 miles... sporty!
I always used a Y-cable off the rear 7-pin. I connect the cable before loading the TC and leave it coiled on the SuperTruss. Once the TC is loaded, I run the cable along side the camper to its plug.