Brian, I have four 1/2" opening and all have ball valves. Some cooks may only require 1+ open and sometimes maybe 3 open, but not too often. Different smokers may work different but that is what I have done with all of them I've built. Just my $.02.
my avatar swiped fatties from the plate....look how sorry he is.
NB Bandera with mods
Weber 22 .5" x 2, 26.75" x 1
UDS x 3
Created "The Great Spam Revelation of 2011."