I'm stretching my memory back to before we got a solar panel. We did boondock for four days in late Septembers here in northern Alberta and BC. Two batteries. They were not quite adequate. But they were certainly half adequate so your four should do for the needs you mentioned. We never run the furnace all night. But you are at least 1000 miles further south so your furnace needs should be modest.
Now that we have a single 100 watt solar panel the batteries are always above 80%. Never plug in, never use a generator, though we do have a 1000 watt one to run the home furnace in a winter power failure, we never take it camping. I think you could save money, noise and gasoline by getting a $200 solar panel kit instead of a generator. Generators are necessary only for air conditioning.