Help with furnace please

Your model the Tstat cannot go below 60 degrees. My question is, why would you want it colder? As you have found out, you set it at 60 degrees and the Roof top Heat Pump will heat your coach to that 60 degrees or any higher setting. Atwood determined that on their Heat Pumps, the low outside temp kick off of the Heat Pump will be 45 degrees. That means once the Outside ambient temp gets below 45 degrees your inside LP furnace will come on automatically and the roof top Heat Pump will kick out. After the Outside ambient rises above the 45 degree mark, the furnace will kick out and the Heat Pump will then engage again until the outside temp drops below 45 degrees. A Heat Pump reverses the flow of coolant (410A) to HEAT instead of cool. They are not efficient below about 36 to 38 degrees outside ambient temp. It requires 120 volts to run the roof top unit in either mode. The furnace is 12 volt operated. Doug

You can disconnect the furnace from the existing Atwood tstat system and install a furnace only tstat on a wall close to the furnace that would go lower. That means your Heat Pump would have no Auto furnace backup connected to the original tstat. You would have 2 separate tstats, one for each appliance. The standard Suburban wall bi metal tstat also has a bottom setting of 50 degrees. This LCD tstat link shows an after market that goes down to 40 degrees.

https://www.zoro.com/honeywell-low-v-t-stat-nonprogrammable-th1100dv1000/i/G7493613/?gclid=CPDYoJOh9M8CFQUuaQodaI4JBw&gclsrc=aw.ds