Rotisserie cooking produces juicy, flavorful meat due to the slow rotation of the meat on a spit, which allows the meat to baste itself in its own juices. Boneless prime rib, a popular cut for rotisserie cooking, is cut from the rib section of the cow and is a rib eye or standing rib roast with the grade of “prime” from the USDA. Prime grade is the top grade the USDA bestows, denoting beef with good marbling from well-fed cattle. Though you can season the meat before placing it in the rotisserie, it's good enough to stand on its own.
Take the prime rib roast out of the refrigerator and set it on a plate. Cover it with plastic wrap and let it sit at room temperature for 30 to 40 minutes.
Season the prime rib with salt, pepper and garlic powder, to taste.
Set up your grill for indirect, low heat. If you are using a gas grill, preheat the grill to high and then turn all of the burners to low. If you are using a charcoal grill, build and light your charcoal either to one side or around the perimeter of the grill.
Preheat a large skillet with 2 tbsp. of olive oil over medium heat.
Sear the boneless prime rib in the skillet for 3 to 4 minutes on each side to create a crust on the outside.
Place a drip pan in your grill directly underneath the rotisserie unit. In a gas grill, place the drip pan on the lowest grill grate underneath the rotisserie, which will block the heat from the burners to help provide indirect heat. In a charcoal grill, place the drip pan where there is no charcoal.
Put about 1 inch of water in the drip pan to create steam while cooking. Add other flavorings to the drip pan, such as wine, beer, broth, herbs or spices, as desired.
Attach the prime rib to the rotisserie unit and ensure that it is balanced for even cooking. Turn on the rotisserie unit.
Close the lid of the grill and cook the prime rib until the internal temperature of the meat reaches 135 degrees Fahrenheit.
Cover the roast and let the meat rest 20 to 30 minutes, during which time the internal temperature will rise about 10 degrees. Slice and serve.