In his book, Field Guide to City and Suburban Survival, Tom Brown, Jr. talks about the many ways there are to stay warm inside of a building that is not heated. I think he might even mention using a tent inside a room.
I think it's a great idea. Would I do it? Absolutely!
We even have a small tent that is, roughly, the size of a double bed. In a worst case scenario, I might even pitch it over a box spring and set my mattress inside and leave it up all of the time.
The thing is, this isn't such a novel idea. People used to use bed curtains back before there was central heating. Bedrooms weren't heated, and people stayed warm by snuggling, by sleeping in small, curtained spaces, and by using thick quilts and comforters.
Since we started using our woodstove for heat, I've found that I sleep better in a cold room. Would I sleep in a tent if my house were cold? Yep.
But, then, maybe, I would redesign my sleeping area and put up some pretty curtains to surround my bed, because a tent would be cool, but waking up surrounded by luxury - even when the reason I have it is because money is tight - would be oh, so much more fun.
I could see having something like this in my bedroom. What about you?