Just for thought.......I have a BBQ smoker that we built approx 10yrs ago out of a 300gal fuel tank. We patterned it after the local "BBQ masters". Anyway, the tank has a divider built in the bottom which sections off approx 1/4 of the tank to be used for the fire box. A grate was placed over the firebox that allows you to grill over an open wood fire if desired. The rest of the tank then is used for smoking. The coolest thing about the design is the exhaust was placed on the opposite end of the tank from the fire box at the bottom. This makes the smoke/heat from the fire go up over the divider and then down through the meat before leaving the smoker. Some people still look at it and say that it won't draft that way, but it does. Actually it works really good......with NO hot spots. It has been my experience that smokers with exhausts on the tops tend to have hot spots near the exhaust outlets.
I have plans on making a bigger one out of a 500 gal LP tank as you can only fit a whole pig on it. Now, someone else has to make the beans and taters;-).