I also have a big chief. The problem is it won't get over about 160 degrees. That's the reason I never used it on meat (great on fish). It just doesn't get hot enough. I replaced it with a masterbuilt.
Yep the Big Chief doesn't get hot enough to smoke the roast. But you could put it in for a couple pans of smoke to flavor it. Then move it to the oven. I have done a couple rump roasts in my Smokey Mountian and they tasted really good BUT were not very tender after smoking.