I have done it but I usually find that the effort involved is massive compared to the gain, mainly because I either have to pick between frozen ground or muddy bog, both are very hard to dig through, consider two hours to make a decent sized hole and two hours to burn wood to make coals, this is assuming you have a decent shovel.
That is four hours of fairly heavy work just to make a fairly light heat source at night. I'd usually go for other things like making clothes or secondary insulation for a shelter. I think it would be a lot better on a sandy area where you can make the hole in minutes. I should try it on one of the local beaches, I'd like to know if you can get a heavier burn without too much focus by digging a bigger coal and adjusting the depth of the coal+dirt and or using reflectors like al foil, has anyone adjusted the 4/8 depth and how did it work?
Lately I have ben making them in stages, I dig a small hole of decent depth and burn in that while doing other things and periodically digging out the bed from the other end. You need to take care when digging around a fire, I generally just let it burn down to coal while doing something else, do some more digging, pile the dirt around the fire part to dry or thaw, throw on some wood and do something else. It takes a long time though, again mainly the ground is horrible.
I am wondering if it would not be more efficent to forget about the hole and just build a platform bed right over a layer of coals between a dual layer of rocks. There are lots of natual rock piles easily found though in the winter it can be very difficult to free them from the frozen ground.
-Cliff
