This is an old trick I've used countless times in the colder regions while on trains..especially on the highline. You take a steele spike bucket and punch holes on the bottom for air. Put rocks in the bottom several inches thick.. ( bigger=better) build a fire and keep piling wood on it and fill it up with coals..put rocks on top of that and when it glowing take a 2 by 4 and pick it up by the handle and put it on your ride. It ll radiate heat for hours. Works great in boxcars!