For the last 4 years I do two turkeys on the kettles. A few techniques that I find helpful.
1) Brine: I start brining the morning before and then pull the birds out and rinse thoroughly on Weds. evening. They then go into the fridge uncovered overnight. This not only lets the brine to distribute evenly but also dries the skin which leads to a nice crispy skinned bird.
2) Aromatics: I stuff the cavities, both rear and the neck cavity, with lemon, onion, garlic, parsley, sage, rosemary and thyme. It imparts a really wonderful flavor to the breast meat.
3) Butter, butter and more butter!: I mix up a compound butter using unsalted butter and some fresh parsley, thyme and rosemary. I let this soften and then smear it liberally under the skin all over the bird, including down on the thighs which you can reach with a little work. I then smear it all over the outside of the skin as well. Nothing goes together better than poultry skin and butter. Not only does it add flavor but also helps with browning and crisping.
4) Grill set-up: I fill two chimney baskets as full as possible with lit briquettes and set them on either side of the kettle as far aparts as possible I will then add 1 small chunk of wood to each. I use a small amount of wood as I don't like a heavy smoke flavor in my turkey, just enough to let my guests know that it was grilled. I then rest a drip pan between the two baskets, I have a pan that has a lip that can rest steadily right on the front edge of each charcoal basket so that it sits elevated above the charcoal grate and just below that cooking great.
I run the kettles WFO and try to get the highest temp possible, I've never taken a grate temp, but I would guess that I'm running in the 375-400 range. I'll add another 6-7 briqs to each side about halfway through cooking.
5) Breast side down!: I start my birds breast side down and then flip it over about 45 minutes in. This is a bit unconventional, but it serves 2 purposes.
a) It allows the entire bird to brown, you don't get a soggy bottom and pale thighs and because the bottom is nice and brown it increases the amount of skin available for serving.
b) As the bird starts to cook the juices run down into the breast. I don't know if there is any scientific basis for this, but I read about it somewhere a long time ago, decided to try it and have always been very pleased with the results
Onto the grill
After the flip
The birds are usually done around 3hrs, then come off and rest until everything else is ready which could be anywhere from 45 minutes to an hour.