I use an e-blanket on the floor of my tent and use 2 candle lanterns hung off a line on carabiners with a foil reflector above them. Been doing this same routine for about 35 years. When its below 10 degrees (10 below is about max for me these days) it allows you to read and be relatively comfortable. They only burn for 2-3 hrs. at most before I want them out to sleep.
The concept of a heated tent is very intriguing, thanks for the posts. My wife would love it!