X2 . Leave the furnace on and pack it with extra insulation.
If the 825 is like the 845, You will notice that the 825 furnace does a naturally good job of placing heat under the stove , kitchen sink, and all the way back under the bathroom sink.
***test the area by using a digital remote thermometer, take readings. See where you need some extra insulation help.
Wrap the propane regulator with some type of insulation, keep it from freezing....no gas flow...no heat.
Keep an eye on any water lines that are routed next to an outside wall. That includes those lines under the stove and possibly under your furnace that touch the horizontal wood that hangs over the trucks bedrail. I use pipe insulation and
Reflectix foil If you choose to drain things by the low point drains and blow some compressed thru it , be sure to clear the toilet line and water pump.
When I do it this way, I use water jugs like buzzcut suggests and use windshield washer fluid to flush the toilet and fill the sink traps.
Always carry a hair dryer to defrost a valve if you have to.
Bob