[grecy]

The best way is with a wood stove inside the tent. Yes, it's very common.

You can go fancy with an "Arctic Oven" like this: http://theroadchoseme.com/liard-hot-springs-winter

Or old school with a wall tent like this: http://theroadchoseme.com/haines-pass-camping

[spondylosaurus]

How do you mitigate carbon monoxide buildup? I was always told that stoves in enclosed areas are a no-no, but clearly you survived to tell the tale, so there must be some safe way to do it :P

[teh_klev]

Look up "hot tenting" on YouTube:

https://www.youtube.com/results?search_query=hot+tent+winter...

[jamiek88]

those tents typically have chimney holes!