This is really easy but it is gooood!
In the seafood dept at Albertsons they have a seasoning called Spade L Ranch for beef.
I have found that Winco has the best tri-tip get a roast.
half of the Spade L marinade onto the roast rub both sides. In a sealed container let marinade over night. On a medium flame slap it onto the BBQ. cook both sides for about 15-20 minutes each then cut in half. Let cook to your spec's. I like mine med. rare. So tender that you can have left overs for sandwich on the river. Cut the meat into slices. Great for those who love to BBQ year round.