I agree with using PUGs and relectrix in the windows. Eliminating the air mattress and sleeping on foam will help you a lot. Wear a hat, get some good down sleeping bags and add some wool blankets or comforters.
I cannot imagine running a propane heater all night in a trailer with canvas ends, nor a little Buddy heater unless it is really cold, say below 15 degrees. Making coffee and breakfast takes the chill off nicely. I have yet to use my heater in the hybrid, but I am happy to have one.
For people that like the trailer to stay warm all night, it seems like a travel trailer with hard sides would be a much better choice.