Don't give up, chicken over a charcoal fire is delicious. It takes some time to figure out each meat/wood/rub/sauce combination works for you.
I think the pan (casserole) was not a great idea, you can make great chicken in a pan of course, but, it will be best on the rack. This allows for more smoke and not sitting in the juices.
I like to brine chickens, but, I will often cook them longer if I have brined, the skin renders better and the slightly over-done meat will still have a great texture. Wampus is right, though, if you brine, let the chicken air cure for a bit.
I cook chickens closer to 400F and I don't understand why you would shut down the vents for chicken. Let it run until it's done. Not like ribs, chicken is not like ribs, important to know that.
The SS Platypus, sails again, to the support of the Vets!
"perhaps...but then again...maybe not..."