Check out The Smoke Ring i believe there is a couple of smoker builds using one of those. I would build a firebox inside just above the bottom. Sorta like the Weber Smokey Mountain.
I would go with the double door. Depending on the size I would put the fire box on the inside and have a water tray above it to use as a heat deflector.
Bryon
My original thought was the same to put the firebox inside but i got to thinking that doing that it may actually get to hot for slow smoking.
If you have the correct venting you should be able to regulate the temperature.
Bryon
Double door...easier to load and unload.
Offset the firebox...can add wood w/o opening smoking chamber. You can even separate them some distance by using some metal pipe. It allows the smoke to cool and eliminate some of the creosote before it gets to the smoking chamber.
"Better to remain silent and be thought a fool than to speak out and remove all doubt."