Preheat the smoker to 250°F and set it up for indirect heat.
Make the rub: mix the brown sugar, smoked paprika, dry mustard powder, kosher salt, garlic powder, onion powder, black pepper, and cayenne in a small bowl. Break up any brown sugar clumps with a fork.
Remove the membrane from the back of each rack. Use a sharp knife to cut between the bones so every rib is separate.
Coat each rib in a thin layer of yellow mustard.
Season all sides of each rib with the BBQ mustard rub.
Place the ribs on a wire rack, bone side up if possible. Mix the apple cider vinegar and water in a spray bottle.
Place the wire rack in the smoker and smoke for about 2 hours, spritzing the ribs with the vinegar mix now and then.
When the bark is set and the bones start to show on the sides (about 2 to 2.5 hours), move the ribs to a large foil pan.
Pour the Carolina Gold BBQ sauce and honey over the ribs and add the cubed butter.
Cover tightly with foil and return to the smoker for about 30 minutes, until the ribs are probe tender and over 195°F.
Toss the ribs in the pan sauce, move to a platter, and serve.
Notes
Use hot honey in the glaze for a sweet and spicy version.
Store leftovers in an airtight container in the fridge for up to 4 days.