Your Smokette maintains a moist cooking environment so there's really no need for a mop. Traditional stick burners are designed to create airflow over the meat as it smokes. The effect of 12+ hours of air flow (smoke) tends to dry out big meats so some cooks will either mop or spritz the meat to maintain moisture.
Vinegar mops are common to pork as they balance the "sweetness" and rich flavor of pork fat. These are similar to Eastern Carolina finishing sauces which are prepared with cider vinegar, crushed red pepper, salt, black pepper and sometimes a bit of ketchup and brown sugar.
One alternative to mopping is foiling during the plateau (165-170). In this case the meat is mopped with a combination of Vinegar sauce combined with apple juice. The meat is wrapped tightly with foil and finished to a fianl cooking temp. The downside of mopping or foiling is losing the crunchy outer bark.
It sounds like you're on the right road as you say your PB's get better and better. Mop or foil a future butt and see how you like it.
Finally, you can stick with your current method and add a finishing sauce to the pulled pork to re-moisten it. SmokinOkie has a tried and true recipe found
HEREHope that helps.