We are okay down to 15 F without any precautions other than putting a glove over the freshwater drain tap. My next measure will be half inch thick stick-on insulation on the underside below a drain pipe that runs in contact with the metal skin underside. I think your insulated skirting will Keep you okay down close to 0 F if you also insulate critical points. And a 5 gallon container of hot water placed inside that skirting overnight would be a huge help. About 3000 BTU with no losses due to cold combustion air being sucked in or hot exhaust flowing out.
How about putting a gallon of RV antifreeze in the freshwater? Use containers of freshwater for drinking and cooking ; shower when you get home.
