Fire up your gas grill for cooking at 250 F. You will need to cook the ribs over indirect heat, so only light some of the burners. Place the ribs away from the direct fire. Add wood chips or pellets to a smoke box. If you don't have one, just place the wood on a piece of foil. Fold up and seal, then poke a few holes in the foil. Place over the direct heat to smolder and create smoke.
Season the ribs with the rub, on both sides. Transfer to the grill over indirect heat. Close the lid and cook for 2 1/2 hours. Check the temperature regularly to make sure you maintain 250 F.
Remove the ribs to a large piece of aluminum foil, bone-side up. Fold up the edges of the foil to create a 'bowl' around the ribs.
Add the vinegar to the 'bowl'. Sprinkle the ribs with the brown sugar and top with pats of the butter.
Fold the foil around the ribs and seal tightly. Return to the grill and continue to cook for 1 hour 15 minutes at 250 F.
Carefully open the foil (steam will escape and it will be HOT!). Poke the meat between the bones. It should be tender. Also, the meat should be pulled back about 1" from the ends of the bones.
Remove ribs from the foil and place directly onto the grill, but still over indirect heat.
Brush the tops with the sauce. Close the lid and cook another 15 minutes to set the sauce.
Remove, let cool 10 times, slice and serve!