So....I never ran out of 12V power.
But my Dad thought that the trailer was connected to a bottomless fresh water well.
Ran the tank dry after 3 days....but the black tank was almost full, as well.
So.....lucky enough....there was a dump site between campsite movements.
Propane use was negligible as only the fridge was using LP regularly. I fired up the hot water only to wash dishes.
I turned the heater on one night because Dad was cold....but Holy Mackerel....the trailer was warm in about 3 minutes.
All in all....a good dry camping expedition.