We used a Mr. Buddy heater during the day at Road Atlanta 2017 snow fest in my 20' trailer. It wasn't working right and could not keep up. The lack of insulation didn't help either.
We used a propane powered canon heater which could heat a trailer or Mulry's 2 car porta-garage pretty well in 2017. We used it in the 24 enclosed trailer at Road Atlanta this year with the side door wide open. I wouldn't sleep with it but being propane it was way cleaner than my kerosene canon.
Roof A/C units with heat strips seem to need more power for heat than A/C. They are typically 5,500 BTUs but I don't know the amp requirement. We used that in my camper in New Orleans and it worked but we had 50 amp 250V RV power and it wasn't that cold. When I've tried it on limited power it was only a slightly warm breeze.
Additionally, typical RV roof A/C units are 13,500 BTUs but need a lot of amperage to fire up. Modern 16,000 BTU marine A/C units will start off a Honda EU2000 generator. I am not sure why the RV world has not improved the efficiency of their A/C units as you will need a pair of EU2000s or a 3000 watt inverter generator to start a 13,500 BTU roof unit. Hard start kits can get many RV units to start on a 2400 watt Yamaha but that's not a common generator and you don't always need that much A/C.
For real comfort in the camper in cold weather the propane RV furnace is the way to go. Lots of BTUs with minimal power consumption. At some point I want to put one of these in my trailer along with an RV AC/DC converter/charger. The RV furnaces have a 12v blower, propane burner and exterior exhaust. I'd still have a CO detector but this is the safest and most efficient plan.
I will also mention that RV furnaces can have some frustrating fail safes. My "sail switch" has an intermittent issue and if it ain't happy it won't turn on the gas. Older heaters have less electronics but crappy piezo igniters. I replaced/hacked/modded the igniter in an older camper with a battery powered grill sparker which made lighting the pilot WAY easier.
When working properly, an RV furnace is like a heater at home. Set the thermostat and it cycles itself off and on.
Basically I want to wire up the trailer like an RV with mostly 12V stuff that can run off a battery. Use a marine battery for the break-away battery and 12V power source. I picked up a power supply from and old camper and plan to recycle a furnace from an old camper and cabinet mount a 8000 BTU window A/C unit. This should keep my power demands down in a 2000 watt generator range. The A/C probably won't be enough for a truly hot day but good at night.
This still leaves another problem. Most 2000 watt inverter generators have small gas tanks. I do have a 2400 watt Yamaha and the extra power is handy along with the bigger fuel tank. Yamaha ain't as reliable as a Honda though. I also have a 2000 watt Generac I bought for a sailboat as an EU2000 alternative, it is a good for the price but not quite as good as a Honda.
1973 Datsun 240Z