Airedale,
We have done some towing during weather in the teens. First, you can leave the furnace on while traveling down the road. This practice has created a longtime argument about having the propane flowing while driving. For the refrig or the furnace, some people do not like the practice. But we do travel with both on and we are still here. We set the thermostat at 45-50 F mostly for the comfort of the cat that rides in the trailer. I think it would be impossible to hold 65-70 F while traveling.
After you stop for the night with the outside temp in the teens, your furnace will run for hours to bring your inside temp up to the mid 60s. I would suggest sleeping in a sleeping bag or else you will feel cold all night long.
WATER: I would not fill your fresh water tank since most of the waterlines will freeze if the temp is in the teens. Carry water in gallon containers and use those. Use the shower in the RV park. If you have an indoor place to store the unit when you get home then you can probably use your toilet and sinks with water coming from the bottled water. IF you don't have a above freezing temperature place to drain the tanks when you get home, DON'T put anything into them.
When at a park, use an auxiliary heater to help heat the trailer. Plan on buying propane proportional to the outside temp. A 7 gal cylinder should last 2 days in the worst temps.
Take I-70 instead of I-90 till your have to head north. Plan your nightly stops for lower altitudes and not in the mountains.
Good luck and good traveling.
Jim