Yes, my 80 degree inside heat was a mistake in two ways. One it was warmer that day. I think about 45F and I forgot to turn off the heater and when I checked the trailer was at 80F. Too hot!
So time does make a difference as does outside temp. This trailer is empty, except for a scooter.
I think I can conclude if a 7x7x17 aluminum trailer with Refectix and wood floor/wall one could heat it with a 1350 watt electric heater about 32F if left on all the time. Mine does cycle on and off. When at 60f inside it is on 5 min and off 2-1/2 min.
I am installing an Atwood 16K in 12K out propane furnace in a month. I am now sure it will handle any weather without more insulation.
I will be building in beds and cabinets which will add insulation in most areas.