Here's a photo of one I did on the WSM for Thanksgiving a few years ago. I cut the rib rack off, rubbed all sides of the roast w/ hot mustard, seasoned w/ McCormick's Montreal Steak Seasoning, then tied the rack back on with twine. Cooked at 240 for however many hours, until the internal temp hit 130. Had plans to finish it in a 500 F oven, but didn't because I thought it crusted nicely at 240. Just rested it for a half hour or more, and carved.
smokinbadger, since yours is boneless, I would strongly suggest you tie your roast.
There's several schools of thought on roasting a prime rib roast. The traditional English way is to sear the outside first in a hot oven, then finish at a lower temp. Theory here is you get a thicker crust on the roast, if you're into that. Poobah's method looks to follow this train.
The other method is to start low and finish hot. Theory here is that you lose less moisture, and the roast cooks more evenly all the way to the interior. Alton Brown's a big proponent of this method. For smoking, this way makes more sense to me, because IMO it's easier to raise the cooking temp rather than try to lower it from 400 or whatever.
But either way will work. Go for it. I'd suggest you use very little wood in the smoker. Even though I like a heavy smoke on just about everything, for a prime rib roast, I prefer a very light touch.
From my blog:
http://professorsalt.com/2005/11/26/new-thanksgiving-traditions/
