OK, I've finally had a chance to test out the new harness on the truck. I had to replace the umbilical from the Lance to the truck too since it was so corroded and was shorting out. For the last two days of driving we have had the fridge on DC and have arrived at our destination with a full battery and a cold fridge.
The new protocol works like this. I set the fridge to auto, close up the camper and then shut off the valves to the propane before we start driving. When we arrive I open the propane vales again and open up the camper. Unfortunately the fridge doesn't seem to recognize that the gas is back on until I power cycle it. This is unfortunate since I could simply turn the gas back on without going in the camper if I stopped for an extended period and didn't need to go into the camper. But that's good enough for now. I'm confident that I'm not going to run my battery down by driving with the fridge on DC.
Actually, I'm pretty ecstatic. Worrying about whether the food would stay cold with the fridge off while I was driving was a PITA and forgetting to turn it off and arriving with a dead battery was even worse.
For anyone with a Lance camper, install the Lance harness and use the correct gauge wire. You won't be sorry.