I don't believe it's the foil. It's the temperature. Rubbery skin is common when smoked.Most teams I know put the chicken on a grill for the last few moments to crisp the skin.
Pigheaded BBQ Team
Stumps Stretch (Raquel) Eagles Green.
1 -22" Weber WSM, 1 - 18"Weber WSM's
2 - 22" kettles
6x12 Haulmark Trailer