Back to your original questions...
Your furnace should keep the interior of your 5th wheel warm enough that you shouldn't have anything freeze INSIDE of the 5th wheel.
The problems you need to be concerned about are the components that are NOT inside an area heated by the furnace that could freeze.
Low point drains, holding tanks and sewer pipes/valves come to mind quickly.
Unless these are inside a heated storage area (commonly called heated basement) or you have tank heaters or some other kind of protection, running the furnace will not keep these things protected.
2016 Flagstaff 8529IKBS Diamond Package 5th Wheel
Ford F-Series SCREW 4x4
TST Tire Monitor - Sinemate 3500w Gen.
2016 Nights Camped = 44