Preheat your grill to 275°F (135°C) for indirect cooking.
Season the pork belly cubes with the BBQ rub, ensuring they are evenly coated. Sprinkle with salt and pepper to taste.
Place the seasoned pork belly cubes on the grill over indirect heat, and close the lid. Let them smoke for 2-3 hours, or until they develop a rich, mahogany color and are beginning to render their fat.
In a saucepan, combine the brown sugar, honey, BBQ sauce, butter, apple cider vinegar, and hot sauce (if using). Heat the mixture over medium heat, stirring occasionally, until the sugar is dissolved and the sauce is well combined.
Carefully transfer the smoked pork belly cubes to a disposable aluminum pan or a grill-safe pan. Pour the sauce over the pork belly cubes, ensuring they are evenly coated.
Increase the grill temperature to 325°F (163°C) and place the pan of pork belly cubes back on the grill over indirect heat. Close the lid and let them cook for an additional 1-2 hours, or until the pork belly is tender and caramelized, stirring occasionally.
Once the pork belly cubes are tender and caramelized, remove them from the grill and let them rest for a few minutes.
Serve the pork belly burnt ends as a delicious appetizer or main dish, and enjoy the irresistible combination of smoky, sweet, and savory flavors.