Can you give a little bit of details on what you had for heat, how you used it, LP furnace available, overnight low temperatures?
We do pretty well down to the 40s with just one 1500 watt heater with the PUP furnace as backup. Below that, I know the furnace really cycles much more frequently. I wouldn't want to do freezing temperatures with just electric heat.
But you can also augment your tolerance for cold temps with sleeping bags rated for colder temperatures, heating blankets or heated mattress pads, Buddy heaters, etc.
It was 39 and raining. We had a 1500 watt electric heater no furnace. Our AC has a heat select on it but it will more less just drop the temp. a few deg. and maintain that temperature. Heat had been off all day we returned that night to a damp cold camper, it took it a while to knock the chill out.
Our first trip in our popup was to Cosby Campground (no electricity) in the Smokies in October a couple of years ago. We have a propane furnace but didn't know how long it would run off the battery and it got pretty cold the first night. We ended up driving to Pigeon Forge and buying some blankets. Nice and cozy after that.