What temperatures were you experiencing INSIDE the coach? If you are trying to maintain 78 degrees inside then it may not be possible without running the furnace for a long time.
To be comfortable, electric space heaters and an electric blanket can make bedtime very comfortable.
We leave Florida most Winters and head up North or out West and we use our rooftop heat pump as well as a portable heat pump to keep us comfortable down to zero and a little below. Below 30 the rooftop heat pump won't work but our portable unit still works fine. The electric heaters also work fine to heat up a specific area of the coach.