Since there was a request for the BBQ version of the tri-tip oven roast, here it is. (It might help you to read that recipe first.)
First, prepare the BBQ rub. I like this Carolina BBQ rub that I originally made for pulled pork. I found it works well on beef, too. The only change I made was using pure ancho chile powder instead of your garden variety chili powder. This was suggested by a couple chefs and I think it turned out well, but if you already have the regular stuff then use it. You are nothing if not practical. And lazy.
Trim the roast, and then sprinkle on the rub liberally and rub it in. Let it marry in the fridge overnight. Don’t worry, this is an acceptable union under the current law; it’s not like a man marrying a box turtle. Take the roast out half an hour before grilling so it comes to room temp.
For cooking times, follow the recommendations in your manual, esp. if it’s a Weber. My Weber manual was quite accurate, definitely more than the one for my Viking range. Like all roasts, it will be medium indirect, and it will benefit from smoke. Try mesquite. Avoid tobacco. And don’t flip it while grilling.
One problem I had while taking its temperature is that heat from the grill messed with my digital thermometer. I had to remove it from the grill while checking the temp. Of course, use a meat thermometer, not an oral or rectal one. In fact, if using either of those is even possible, your butcher has executed an elaborate ruse at your expense. Always remember: a tri-tip roast has neither a mouth nor an anus. Words to live by.