Prepare the duck legs the night before smoking by CAREFULLY piercing the skin in several areas with a fork or sharp paring knife. This will help the fat to slowly drip away while smoking. By the end of the smoking time, the fat will have dripped away into the water pan, leaving moist succulent meat, with a crispy skin. DO NOT PIERCE THE FLESH, as you do not want the juices to escape during cooking. Rub the duck legs with sherry and let sit, uncovered, in a flat bottomed glass dish overnight in the refrigerator.
The next day, coat the duck legs in a thin layer of yellow mustard. This will allow the rub to adhere to the duck and will help develop a zingy tasting, crispy skin. Sprinkle the rub over the mustard and let rest for 1/2 hour.
Meanwhile prepare the Keg for indirect grilling at 200°F, fill diffuser kit with water and add a handful of wood chips.
Place duck legs skin side up on the lower rack of the Keg, over a filled water pan.
Adjust temperature as required. Add a handful of soaked cherry wood chips every hour for the first 4 hours of smoking. Have the fruit juice mop ready in a spray bottle. Spray duck legs liberally with the juice every hour. Continue cooking until the internal temperature of the duck legs reaches 165-170°F. Serve with Sour Cherry Sauce on the side.
In a medium saucepan, combine wine, port, sugar, ginger root and orange zest, and bring to a boil over high heat. Reduce temperature to a lively simmer and reduce by half, about 10-15 minutes. Scoop out the ginger and orange zest. In a small bowl, stir together the corn starch and vinegar. Whisk this mixture into the wine reduction and stir until slightly thickened. Add the drained cherries and heat through.