We run our furnace about 5 to 10 minutes in the morning to bring the TT temperature into the 60's. After cooking and sunshine heating we are set until the next morning.
The biggest issue is the phantom circuits that run the frig, detectors, TV booster and etc. I have measured over 1/2 amp of these sneak currents depending on which device was turned on. I estimate my battery would last two or three days, maybe more since we converted to LED lights.
Out West there were several areas where boonedocking without power was your only option. I works for us for a day or two.
Off-grid camping reminds me of my old canoe and tent days, only with a large aluminum tent.