I have slow smoked and grilled indirect on a roti. My favorite way is slow smoke. My wife prefers the rotisserie version. If you have Weber's Big Book of Grilling by Jamie Purviance, try the herb crusted prime rib on the rotisserie; it's fabulous. If you are an America's Test Kitchen member check out the Cook's Illustrated piece on slow roasting prime rib; it adapts to a smoker perfectly.
I slice several garlic cloves, put slits in the fat cap, and insert a slice into each slit. Usually do from six to twelve slits, depending on size of the roast. Wipe down with olive oil. Then I mix Kosher salt (1 cup), cracked black pepper (3 T), Rosemary (3T), and Thyme (3T). Pack the mix onto the roast. After sitting at room temp for three hours, I place into the Weber Kettle. Kettle has been setup for indirect with a toss away aluminum foil pan set between the coals. Pour one can of soda, beer, or use water, into the pan. I use a roasting rack, fat cap up. A!so use a temp probe. When the temp in the center hits 130° F, I pull the roast, tent it with foil, and let it rest for 20 minutes or so.
I like “Hawkeye” Dave’s method!
There are so many ways to do a roast like that, sometimes I go back to basics and just use a fresh herb rub with garlic, rosemary, oregano, salt and pepper, indirect on the kettle with a fist size of cherry or pecan.
Agree on monitor of temp!