If you're stationary for the Winter and have dedicated 120V, I'd start using electric heaters.
Also, I replaced my propane RV furnace with a Sportsman heater. They are no longer made but similar fish house heaters are available. They heat well without any electricity, basically, a gas ring in a big can. I do use some small fans to move the heat around but once my rig is warm, I turn down the heater to idle. This is the third RV I've had this Sportsman heater in and it is far superior to the typical RV furnace. I've tested it to -15f for a few days. I'd suggest you try to find something similar so you don't fight battery charging all Winter.