On my older MH it said that the optional heat in the A/C was intended strictly for getting rid of the morning chill. I'm pretty sure I settled on the furnace for the night.
The heat strip in the AC is a high power draw, probably pretty close in amp draw to the compressor that is used to cool the air.
If you are parked hooked up to shore power, I would use it and save the LP.
If you are on generator, I would use the furnace.
Found this on another thread, might be helpful:
My "Dometic" Briskaire Roof Ducted Air Conditioner 13500 btu draws
960 watts in cooling mode with low fan, or 8.7 amps.
Here are some other measurements from it.
222 watts fan on low no heat
250 watts fan on high no heat
1408 watts heat strip on with fan set to low
1422 watts heat strip on with fan set to high
Maybe a different model, but all have similar 'guts'. You see the heat strip pulls more than the A/C!