Williamlatham:

Don't know how much latent heat an extinguished carbide lamp has, but the candle or mini oven between the legs still pose an exposed flame problem.

Older arthritic people like myself would have a difficult and in my case impossible time squating down tight without being able to move my legs frequently to alleviate pain. In the process of shifting around from time to time, it would be very desirable to not have to worry about my garbage bags, space blanket, clothes or other insulating cover coming in contact with an open flame or high temperature heat source that could ignite them.

The biggest down side will be the bulk of the "furnace".

Bountyhunter