Those folks on America's Test Kitchen showed me how to make a beef roast on the barbecue grill. It wasn't grilling as such, because the roast was set away from the heat, so more like baking in an oven. We don't have a gas grill, and I'm not sure I'd want to mess with nursing charcoal to achieve the required slow cooking for the tougher cut of meat they suggested.
They used a top sirloin roast and rubbed it all over with chopped fresh garlic, rosemary, salt, and pepper. It was wrapped tightly with plastic wrap and refrigerated for 18 to 24 hours before cooking. The grill was set a medium hot, and the roast was seared on all sides. Then, half the burners were turned off and the roast was put on that side to cook with indirect heat. The internal temperature for medium-rare was 125, and once that was reached it's important for the roast to sit on the counter under loose foil for 20 minutes.
If you're craving roast beef and don't want to heat up the house by using the oven, this'd be worth considering. It was tantalizing to hear the cooks on the show carrying on about how nice and tender the meat turned out, but I don't plan to try this method any time soon; it sounds like something I'd do if the power was out and I had no choice. The herb rub sounds really good, and I'll try that some time.