Any of the 1500 watt ceramic heaters will do fine.
On 30 amps I could run one on high and another on medium without tripping a breaker. If I needed the microwave I turned the one on high off long enough to use it. I have in a pinch ran both on high for short periods.
Do remember that if weather is below freezing use only one so that the furnace will cycle and keep the pipes and plumbing bays warm to prevent freezing.
While I am not an expert on winter camping, I did full time in northern Kentucky for 4 winters with some days below zero and did it without freezing up.
There are plenty of things to do to save propane, close all blinds or drapes after the sun drops, that will keep the cold transfer from the cold windows.
Learn to bake in the oven the warmth from that will provide extra heat.
Orient the trailer so the sides with the most windows faces south/southeast so that the sun will track from end to end on sunny days. I actually had inside temps exceed 85 degrees on an 18 degree day from solar gain. Come dark it got cold in a hurry.
It can be done with planning and not break the bank. I averaged a gallon of propane per day the last two winters I had to do this.