i have done a few turkeys on my 18 from 16 to 20 lbs. and I wet brined over night and then dried and i did put Butter under the skin, then seasoned. setup was minion method with a 3 chucks of wood, light types, Apple, Pecan, Peach something like that. I do not used water in the bowl but i do put a pizza pan on top to make clean up easier, and a drip pan for catching the gray juices. i set the temp for about 275 to 325. then rotate the grate 90 degrees every 30 minutes of so. a 20 lb bird takes about 3 to 3.5 hours i do run a temp probe into 2 places breast, thick part of thigh.
they come out great with excellent flavor, and light Smokey aroma.
Enjoy