|Wood River BBQ Team
Here's how we cook prime rib -- actually, I think a boneless rib eye roast is a better choice but both are excellent cuts of meat.
The Lang cook temp we use is 260 to 275 degrees. The internal is 135 degrees (medium rare to medium). The smoke is cherry. We trim some, not all, of the fat and cross cut the fat that's left so the marinate can penetrate to the meat. The marinate is veggie oil, Montreal steak spice and worcestshire and let the meat marinate for a min of 4 hours.
We don't place the meat on the Lang grate but on a rack over a pan of water, spices and wine -- red or white, your choice.
We mop (spray bottle) every 30 minutes with a combination of apple juice, veggie oil, worcestshire and cider vinegar and turn the meat (upside down and sideways) at about 100 degrees internal. At about 125 to 130 degrees internal, we remove the meat, wrap it in alum foil and place in a cooler for 20 to 30 minutes to continue cooking.
A 3.5 lbs piece of meat will take about 2.5 hours but we don't cook by time but by internal temperature using a digital thermometer.
There's probably a bunch of other ways to cook prime rib (do a google search or wait to hear from some of the mates on this forum) but the above, after a lot of experimenting, is what works best for us.