Select a prime rib roast from your butcher that has been dry-aged 28 - 35 days. Trim off excess fat and any areas that appear dried out.
Remove the roast from the refrigerator 90 minutes before cooking. Tie 6 - 8 loops of string around the roast gently pulling the roast into a round shape.
Rub the roast with oil and season with salt, pepper and garlic powder. Do not season the ends of the roast.
Setup your smoker for indirect heat at 250°F using good quality lump charcoal. Place the roast on a raised rack over a sturdy jelly roll pan and cook to an internal temperature of 125°F for medium rare, about 30 - 40 minutes per pound.
Remove the roast, tent with foil, and allow to rest for about 15 minutes. Reconfigure the smoker for direct heat at 500°F. Sear the roast over direct heat to form a nice crust, about 1 minute per side, 4 minutes total. Slice ½" slices and serve with Au Jus, creamed horseradish and some popovers. Enjoy.