Top round roast yields great flavor, particularly when its cooked slowly to a medium-rare doneness. Here's a recipe from America's Test Kitchen. I have not tried this but I trust these guys. Good luck -- look forward to the photos and report back.
GRILL-ROASTED BEEF WITH GARLIC AND ROSEMARY
A pair of kitchen shears works well for punching the holes in the aluminum pan. We prefer a top sirloin roast, but you can substitute a top round or bottom round roast. Start this recipe the day before you plan to grill so the salt rub has time to flavor and tenderize the meat.
6 garlic cloves, minced
2 tablespoons minced fresh rosemary
4 teaspoons kosher salt
1 tablespoon pepper
1 (3- to 4-pound) top round roast
1 (13 by 9-inch) disposable aluminum roasting pan
1. Combine garlic, rosemary, salt, and pepper in bowl. Sprinkle all sides of roast evenly with salt mixture, wrap with plastic wrap, and refrigerate for 18 to 24 hours.
2A. FOR A CHARCOAL GRILL: Open bottom vent halfway. Light large chimney starter half filled with charcoal briquettes (3 quarts). When top coals are partially covered with ash, pour evenly over one-third of grill. Set cooking grate in place, cover, and open lid vent halfway. Heat grill until hot, about 5 minutes.
2B. FOR A GAS GRILL: Turn all burners to high, cover, and heat grill until hot, about 15 minutes.
3. Clean and oil cooking grate. Place roast on grill (hot side if using charcoal) and cook (covered if using gas) until well browned on all sides, 10 to 12 minutes, turning as needed. (If flare-ups occur, move roast to cooler side of grill until flames die down.)
4. Meanwhile, punch fifteen ¼-inch holes in center of disposable pan in area roughly same size as roast. Once browned, place beef in pan over holes and transfer pan to cool side of grill (if using charcoal) or turn primary burner to medium and turn other burner( s) off (if using gas). Cover and cook until meat registers 120 to 125 degrees (for medium-rare) or 130 to 135 degrees (for medium), 40 minutes to 1 hour, rotating pan halfway through cooking.
5. Transfer meat to wire rack set in rimmed baking sheet, tent loosely with aluminum foil, and let rest for 20 minutes. Transfer meat to carving board, slice thin against grain, and serve.
THINK THIN When slicing this roast beef to serve, peel off wafer-thin slices of the rosy meat with your knife. (A slicing knife is ideal for this task.) Cutting extra-thin slices will make the meat seem even more tender.
The Editors at America's Test Kitchen (2012-10-12). The Science of Good Cooking: Master 50 Simple Concepts to Enjoy a Lifetime of Success in the Kitchen (Cook's Illustrated Cookbooks). Boston Common Press. Kindle Edition.
