I actually bought one of these a few years back:

http://www.zodi.com/Consumer/zodihotvent.html

It's a great concept, and worked moderately well. The propane cylinder seemed to freeze up a bit or something in really cold weather, which appeared to reduce its output. I also tried running it off a big 20 lb tank, which IIRC worked better. I'll have to dig it out and fiddle with it a bit more.

In my quest to heat vehicles/tents/etc, it is the only thing I found that I felt comfortable with, because of its outdoor combustion and venting.

David