Most RV parks are closed in winter.
The 12v fan in my 18k BTU propane furnace will draw down my 2 AGM camper batteries in a day or 2, especially since I keep the heat on low for my dog during the day. The furnace also goes thru quite a bit of propane so I have 2 20lb (5 gal.) tanks.
Due to snow, clouds and reduced daylight hours in winter, solar is not reliable. I run my Honda 2000 watt generator every other night or so with the furnace turned off so it won't drain the batteries at the same time I am trying to charge them with a smart battery charger. I then heat the camper with an electric space heater.