In a medium bowl, stir to combine salt, brown sugar, pumpkin pie spice, mustard powder, garlic powder, onion powder, and black pepper.
When ready to cook, set grill temperature to 250 degrees F. Preheat with the lid closed for at least 10 minutes.
Rub the ribs generously with the dry rub on all sides.
Place the ribs on the grill and cook for 2 hours. Remove from grill and carefully wrap each rib rack in a layer of foil. Return the ribs to the grill and cook for another 1 1/2 hours.
Remove from grill and let rest 5 to 10 minutes before cutting and serving.