Not exactly an answer to your question, but an alternative to heating at night, and it works very well for me:
I run my Honda EU2000i all night, and have a cheap Wal-Mart heater, one that has THREE heat settings (wattages). I run it on low, which is 600 watts, and it keeps me toasty all night.
A friend does the same with his EU1000i.
I sleep much better with the gen and heater rather than the propane furnace running, because the furnace is loud and wakes me up when it cycles all night.
This won't work in campgrounds with quiet hours and camp hosts that patrol for noise.
I've done this in dispersed camping areas and USFS campgrounds that were mostly deserted due to camping there in the late fall.