If I were to recommend something... I'd buy a Big Buddy heater and a six pack of 16 ounce Coleman propane bottles. Make sure you have some ventilation in your rig, keep the Buddy heater away from anything flammable, and note that burning propane does add water into the air... but it can come in handy, because it may not be as nice as the RV's furnace... but it is nicer than getting sick due to cold.
Long term, you really need two batteries. One battery won't last the night, and if it does, it will be below 50% SoC and take damage. A few weekends of this, the battery will be completely trashed and only useful for a core charge refund.
After that, check your converter. If it is not a multi-stage converter, replace it for a good multi-stage unit (preferably a five-stage with a pendant, so you can equalize the batteries.)
From there, a generator. Two Honda eu2000i units and a parallel cable is a setup which offers the most flexibility. A 3000 watt unit is also an alternative, but requires to people to heave around.
After that, solar. Solar panels and a decent charger (I always recommend MPPT controllers, since they can feed the battery the charge it needs at the state of charge, be it float, bulk, absorption, or desulfation.) This will also ensure that while your rig is in storage, the batteries will be always topped off and ready to go.
After that, it really goes to personal preference.