Tom, it's almost impossible to get crisp skin when only using a smoker. Most folks will also use their charcoal or gas grill to get the skin crisp. The other option is to take the skin off the piece and get all the fat you can off the skin. Some use a bic blade shaver to do this...others if you are more skillful use a very sharp knife. If you can get your smoker to goto between 300-350 that will help.
