most rv's are not made for cold (or hot). They are not insulated worth a darn. Mine had haphazard placement of insulation in the ceiling (think none in some areas). Furnace takes a lot of power so I would think (know) that battery will be long dead by morning. Most factory convertors will not charge a battery quickly so I use a battery charger to pump them back up.Walls are thin and most have single pane glass so very little R factor there. Tank heaters will take plenty of power, Mostly 12 vdc so a battery bank of 4 or more may be necessary and solar if you don't want to hear a genny run all day. I know your neighbors don't want to. I'd head for temperate climes.
