I'm not familiar with your set-up. When I do Prime rib I score it first, then coat with worcestershire, Montreal steak seasoning and granulated garlic. I try to do this at least a day ahead, 2-3 days if possible. Then I cook it on my Weber rotisserie at around 250-275. I like to use mesquite for the smoke. Mine usually gets to rare in about 3-4 hours. I have only done them boneless however, I like to fix up the ribs as appetizers. I'm not sure how the cook with the bones on would affect the time/temp considerations.
Another tip I've heard is to cut the bones off, apply your seasonings of choice and then tie the ribs back on. I've been wanting to try it this way, but don't cook Prime rib all that often, big bucks you know.
Good luck in any case, I'm sure you will get all kinds of advice from the helpful bro's here.