I've been wanting to smoke a Prime Rib roast forever, and I've been looking at some small ones at my local grocer. Most of them have a huge fat cap on them, though. I'd like to get one and use a garlic paste rub that I found, but I don't know if I should trim down the fat cap or not first. I also want to make an au jus out of the drippings, so I'm really not sure what to do here. Any advice?