All of a 24.1's fresh water plumbing is above the floor in the heated space. In addition the furnace's duct work runs right next to all the lines. Thus if you run the furnace your fresh water system should be fine.
The problem here is that if you do use your furnace your propane isn't likely to last 4 days (when we camped in freezing wx we used a full tank in a bit more than 48 hours--a weekend). You'll want an extra tank or two--or a mobile service to refill.
The waste tanks are below the floor with heat pads on the bottom. Your biggest problem with these is likely to be the drain plumbing to the valves--putting some RV antifreeze down the drains should help out here. Since the valve area is so small you may only need a 100W or 60W lightbulb in there to keep it warm (a real lightbulb--not an LED one). Something like
this guy (Amazon) would work to keep the drains warm enough to not freeze.
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