1. HP's do NOT work on LP---120 ONLY
2. HP's (RVP old style like the OP has), IF the set HEAT temp is MORE than 5 degrees (the inside temp is 55 and you set the tstat at 65), the FURNACE (runs on LP and is a separate appliance and not part of the HP, will come ON and heat the RV. Once the inside temp is within 5 degrees of the set temp (in this case 60 to 61). the furnace will shut OFF as the HP comes on and Heats the final 4 to 5 degrees. Once the set temp is reached and the HP is left ON, the HP will come on when the RV cools and will heat up the RV to its preset temp.
3. The NEWER RVP HP's BOTH the HP and the furnace will come on in the greater than 5 degree separation. Once it reaches the within 5 degree the Furnace will drop out and the HP will complete the heat cycle.
4. RVP does this because they realize that it would take a LOT longer to heat up an RV with just a HP if the 5 degrees is greater. Doug