Agree with FunVet and BlackDog...........some questionable methods on here every once in a while.......overthinking things, IMHO.....
Anyone can build these things however they want, but the Norcoredneck design is hard to beat.
Evenly spaced draft holes, 2 with pipe caps, 1 with a ball valve. Hard to beat this. It works like a charm. I just left the holes open, and I cover them with refrigerator magnets instead.........very cheap and reliable.
My next advancement is a homebrew draft controller which will attach to a pipe nipple and valve on one of my draft holes. These things burn rock solid all on their own, but a draft controller just gives a little peace of mind on an overnight cook, when I want to sleep, rather than anxiously feel the need to check the cooker for temp.
p.s. Don't add a door to the firebox.......too much potential for air leakage and draft problems. If you have a big enough basket, you will never have to add coals or wood. Use the smoking wood sparingly......only a couple chunks needed for a 12 hour+ cook.