I went ahead and bit the bullet and bought a new Lance wiring harness and had the dealership install it in the truck. I made sure to tell them multiple times that it was important to have 8 gauge or better from the truck battery to the harness, in case they needed to go longer. They did come up a bit short, needed a little extra and bought themselves some 8 gauge to finish the install.
I just hope the run isn't too long.
I'm dying to drain the camper battery, put the camper on the truck and test it out with the fridge running on DC. But I can't do any meaningful testing until the week after next at the earliest. :(