I can only describe personal experience.
When we got our firts Class A (1977 Pace Arrow 27 foot), we couldn't wait to try it out, so to Wood Lake, in the mountains above Augusta, MT, we went.
Beautiful! Total solitude, good fishing, dark and quiet.
The coach had one 8D battery, the HUGE 12 volt beast. That will last all night, right? WRONG!!
At 3 AM a strange noise woke me up. It was the furnace blower trying to run, and failing due to low voltage. That huge battery was almost totally dead! The temperature in the coach was about 35 degrees. I had to get up and start the engine to get enough power to start the generator.
Lessons learned:
1. Run the generator before bed to ensure that the battery(s) are FULLY charged!
2. The furnace is a power hog!