Using a spice mill grind the peppercorns, mustard seed, and fennel seed into tiny pieces. In a small bowl combine the ground spices with the remaining rub ingredients.
Score the fat on the ham by making crosshatch marks about 1 inch apart and ½ inch deep. Season the ham all over with the rub. Cover and refrigerate for 8 to 12 hours. Allow the ham to stand at room temperature for 30 minutes before grilling.
Prepare the grill for direct cooking over low heat (250° to 350°F).
In a medium bowl whisk the mop ingredients.
Following the grill’s instructions, secure the ham in the middle of a rotisserie, put the rotisserie in place, and turn it on. Let the ham rotate over direct low heat, with the lid closed, until the internal temperature registers 140°F, 2 to 2½ hours. (Note: If you do not have a rotisserie, grill the ham over indirect low heat(250° to 350°F) for 2 to 2½ hours.) Baste the ham three times with the mop during the last 30 minutes of grilling time. When the ham is fully cooked, turn off the rotisserie and, using barbecue mitts, remove the rotisserie from the grill. Let the ham rest for 15 minutes before carving. Serve any remaining mop with the ham, if desired.