Convenient cold-smokers can be made from wooden barrels and metal drums, provided that the fire or heating element is external. Metal drums conduct heat better than wooden barrels, and therefore run cooler, but they are not as quaint as, for example, a used Jack Daniel’s whiskey barrel.
If a vertical smoker is desired, cut a hole in the bottom to accommodate a stovepipe or other smoke conduit from the heat source. Then remove the top of the barrel and install racks or bars for holding or hanging fish or meat. Next, fashion a lid for the barrel and drill or cut holes for the smoke to escape. (A smokestack is not necessary, but it will look better if you are setting up a more or less permanent smoker.) Usually, a piece of plywood cut a little larger than the top of the barrel will make a satisfactory lid, and vent holes can be drilled directly into the plywood. Drill only a few holes at first, then add more if needed.