I obtained 32 of these steel tubes (they are from the center of a roll of sheetmetal.
1/4" plate 1200mm long with 600mm diameter.
So far this is the design we have which is most efficient to build.
33% volume of the cooking chamber, we cut 1 tube into 3 pieces to make 3 smokers this size.
Seems to work perfect
Very nice craftsmanship.