Allen, how will a Coleman HP run like this with the condenser coil mounted temp switch which is set for 18 degF. With the 18 degF and the approximate 20 degF approach on the outside air, they will shut down the compressor around 38 degF. By the time the out side air is down to 40 degF, the outside coil is a ball of ice and you get no more heat to the interior coil.
A residential unit is designed to run to colder temps than and a RV unit. Don't believe me call Coleman.
I am a mechanical engineer and worked in the industrial refrigeration field since 1970 both in service and engineering.
Ken