I do the chops more often than the whole roast, but when I do a roast I treat it like a loin since its farther down.
Brine it and WSM it at 250- 275ish till 130 than a sear at the end. I take it till 140deg. Indirect on the kettle also works.
Found a detailed way here http://www.smoking-meat.com/december-6-2012-smoked-pork-sirloin-roast
HTH