For the marinade, dissolve 100g salt and 50g sugar in 250ml apple juice, then add roughly 100ml water. Wash the pork neck and place in a container. Pour the marinade over the meat and refrigerate overnight, or use a meat syringe to inject the marinade throughout.
Prepare the grill for medium indirect heat with a drip tray positioned between the coals. Pre-soak smoking chips in water if desired.
Remove the pork neck from the marinade and pat dry with paper towels. Reserve the remaining marinade. Rub the meat all over with a portion of sriracha sauce (or mustard) in a thin layer, then evenly spread the BBQ rub on top.
Pour the reserved marinade into the drip tray and fill with water until the liquid reaches about 1 cm high. Place the meat on the grill grates directly over the drip tray, sprinkle with smoking chips, and close the lid. Grill at medium heat (approximately 150°C / 300°F) for 3 hours, or until the internal temperature reaches 63°C (145°F) at the thickest point, measured with a meat thermometer.
While the meat cooks, squeeze the juice from 1 lime and mince 1 clove garlic into the balsamic vinegar, then stir in the sweet chili sauce. After 1 hour of grilling, brush the meat with this glaze. Repeat every 30 minutes, adding more smoking chips as needed.