If it's dry, it's likely overcooked. You may need to get an instant-read thermometer (or a remote thermometer) and monitor that temperature closely the first few times you smoke it, and make sure it doesn't get overdone. 165° is a good target temperature for doneness. Once you get the hang of it, you can usually guess how long it will take to cook and be pretty close. You might also want to pull them out of the refrigerator at least a half hour before you put them on the smoker or grill, maybe more like 45 minutes, so the outside doesn't get overcooked and the inside remains raw.
One recipe I've seen calls for 225° smoker temperature and three hours on the smoker, until the interior reaches 165°. Anything higher than 275° is more like baking/roasting.
When I make chicken pieces on the kettle, I do them over indirect medium heat (coals in baskets along the side, chicken in the middle), and it only takes about 35-45 minutes (depending on the size of the meat) for a crispy skin and juicy insides. Dark meat is less sensitive to overcooking than light, I've found. I will sometimes use one or two large chunks of applewood on the coals (never wood chips, since they burn/ignite and expire too quickly) which gives the skin a really dark color and enough smoke flavoring. I prefer this to messing around with a smoker for chicken, as it's usually only a couple of pieces for us.
I never wet brine the meat--brining is not done to add moisture, but to season the meat. I prefer to season it dry with a good rub. (Some call this "dry brining" as you can let the seasoning sit for an hour or two to absorb into the meat.)