The brine will help, as well as removing the chicken when the IT hits 165...lack of brine and perhaps letting it go a bit too long likely contributed to the dryness of the meat. As for brine, there are several good recipes on the forum, but I usually just use 1 gal of water, 1 cup of kosher salt, and 1 cup of dark brown sugar. Be sure to fully dissolve the salt in the water, and you can add any additional herbs/seasonings to the brine. I often add Italian herbs, garlic, etc. For a small chicken, you would need only 3-4 hours for the brine before you rub and smoke.