I just spent my first night boondocking in cool weather in my RV.
It is equipped with 875 amp-hours of battery storage (Walmart 12 volt deep cycle batteries @ $0.60 cents per amp-hour)--and they were at 100% state of charge.
I decided to see if I could use the batteries to keep warm.
The low temperature for the night was 6 C (42 F), so there was no risk of freezing damage. Just to make sure I set the air conditioner "heat strip" to cut in at 5 C. (40 F)
My RV has a sliding cloth "door" for the bedroom. I shut it to reduce the area to be heated. I also put a "vent pillow" both the vents. I fully closed one window blind--but left the other 1/2 open.
I connected a 466 watt oil filled heater and set it to keep the bedroom at 18 C (64 F).
My batteries lasted the entire night and did not go below 50% state of charge (12.1 volts)--and the kitchen area got to 12.8 C (55 F) so the heat strip did not "add to the load". I have a kill-o-watt meter--and I clean forgot to put it "in the circuit".
Today I drove for about 3 hours. It was a dull day so the best my solar system did was about 5 amps of output. The solar panels returned about 40 amp-hours in total. I run my fridge on 110 volt when I trundle down the road, and recharged my laptop batteries. I also ran the fridge for one hour while the RV was parked (motor *not* running, of course). The "house" batteries got to about 12.5 volts (measured "under load" at a C40 rate) This represents about 90% of fully charged.