First I STOLE this idea!
Tried first with my tailgating CB-500 & it worked!
Now my big grill with a 36 X 16 cooking area is a 10+ hr smoker.
You just need a few bricks and a pan to act as a heat shield.
Make a "fuse burn" with wood chunks covered with charcoal, the one you see burned 8 hours when the full fuse is placed will last 12 hrs.
Only cooked one 7 lb butt.