try a sawdust stove - great for warming up a teepee/chute shelter.
basically you cut a hole in the base make some legs, then ram pack sawdust/wood shavings down arounds a broom handle/dowel. take the handle out anfter packing then light the base through the bottom hole. teh holes restrict the airflow so you get a good steady slow hot burn.
that size tin should work for 6-10 hours
you could also use it as a camp oven.