I do mine slow and low with water in the pan. They don't take near as long since you typically take them to 125-135 depending upon how you like it done.
I take my chefs knife and stab in to the top fat cap, pull on the blade and poke a clove of garlic in the hole. I do the clear across the top side. Usually 3 rows about ever inch or two. The goal is to not go deep in the meat. You want the clove sitting just under the fat cap.
Then season the whole prime with Cavanders Greek seasoning. All sides and to the point the meat is green. Then get fresh rosemary strip the leaves off and crush them. Put the leaves on and wrap the prime with plastic wrap. Let it sit for a day or two in the fridge before smoking.