If you can swing the extra time, let the chickens sit in the fridge uncovered for 18-24 hours after brining. This will allow the skin to dry and will help a lot in avoiding the rubberiness. Also, the minion method is to maintain your coals over a long period of time on low and slow cooks. Not what you want to do with chicken. Fire off a full chimney of lump, then dump it in and add another chimney of unlit on top of it. You want all the BTU's that puppy can pump out. Run all vents wide open until you get to 400˚. Then start shutting the lower vents by maybe half, but in all likelihood
you're going to need all the air the coals can get to maintain that heat.