I also recommend a vinegar spray and then a rub that's heavy on salt be applied to the skin.
What I do on my offset with chicken pieces, is once the chicken hits 160°, I place them skin side DOWN on a rack inside my firebox, where the temp is 425° or more.
Only takes about 1 minute and now it's crispy.
Also, for those of you that brine first. After you brine - put the chicken pieces or whole birds on a rack over a cookie sheet and cover loosely with paper towels and let "drip dry" in the fridge for 12-15 hours...then it's easier to get crispier skin at the end of the cook...its WAY harder to get crispy skin if the bird goes right from the brine, to the rinse, to the smoker.
Hope that helps!