Okay, we have done it. My brother had an old chevy panel truck around a 1964 or so. We took a freon can can cut and welded a door and ash pan with the flue that went out the back door window. Yes the fire box was inside.

Worked good with wood. One winter we were drinking out to Colorado to go skiing and sleep in the van. We saw a freight train loaded with coal and stopped and walked down the tracks picking up coal lumps that fell off. We had a bucket full in no time. it burned a lot longer than wood but stunk. Still wouldn't last the night. We camped out at on Rt6 at Loveland Pass about 12'000. one day was the biggest swing in temperature I have ever seen. -19 low the next day was 79 for the high at A-Basin.
Full disclosure, we were in high school at the time.
In this day and at my age I'm not going to mess with trying to keep a fire going all night with wood or charcoal. That little diesel hearer is cool and a bargain at the price. I would prefer propane over diesel and that would be the Buddy. We tent camp in the mid 20's and am hoping we can push that to the high teen's in the teardrop. We'll see this winter, we are planning a trip to the Grand Canyon over New Years.
Todd