Kevin, I was thinking of a heater a while back but have decided at least for a while to forego it for the time being. I live in the South on the island Ocracoke and for local use or heading up North in warm months I haven’t really needed more than what I now use. Before this CLC teardrop I built a classic TD out of birch plywood for my daughter who lives in Park City Utah. We share it usually in October or May and she uses it all but the really cold months. It’s not insulated but it’s bigest problem is sweating inside in cold weather when camping at 5,000’ or greater where the night become very cold. That teardrop as well as the CLC one demand that you have ventilation when inside and of course when sleeping. In the second year of use she and her husband had it closed up tight on a cold night in the 20* range and woke up gasping for air before opening a vent some. That said what we do now on cold nights is sleep in long under ware with a light ski beanie. She has a thick feather comforter to pull up and get under. If that is not enough add a 30* down bag. You said you were considering something electric and if you will have 120v at hand you have a lot of options from an electric blanket to a very small safe heater. That has never been an option for us as we go off the grid. The best heater I’ve found runs on propane and a low current draw electric circulating fan. Propex HS2211 is what I found and from what I’ve read it’s safe and mounted underneath. It’s not cheap, $825 but from what I’ve read I would trust it. It’s web page offers a lot of information and I don’t think “it’s made in China”. I would post a picture but this site is so bad that I usually loose everything whenever I attempt and no help fron their webmaster.
Bill