Picture a gas oven with stove top, then rip everything off it and leave a shell, what you are left with is a sealed oven with door, racks, a whole in the bottom where the gas burner was (so the smoke can come up it) and a chimmeny. PERFECT.
With smoking you aren't really looking for alot of heat just quality smoke.
Anything that drips down (marinates) will just be like a normal oven with a drip tray at the bottom. you can add in hooks at the top for hanging things and remove the racks.
