Clarification on the batteries. I was on a ferry for 2 days and had to shut off the propane so the fridge was straight DC power and it was full/ warm outside and opened up regularly to get food out.
I'm pretty sure the camper would run for a few days on DC / propane without recharge.
Correct, the wiring is heavier on the camper pigtail than the wires in the extension. My extension looks like the shop hand made them though and is 12 ga wire. Same 7 pin plug though on the camper. . Unless mine was changed. Fwiw I have run all summer like this with no elect issues.