Trim excess fat off tri tip (see video for visual).
In a large zip lock bag add marinade ingredients and the trimmed tri tip. Seal tight and shake well to mix. Marinate for two hours, (up to 6) in a dish in the fridge, remembering to flip the marinade and bag halfway through the marinade time.
Remove meat from bag and discard marinade. Pat meat dry, remove excess rosemary and chunks. Mix the salt and pepper in a small dish and season roast.
Pre heat the smoker to 225 degrees F using a fruit wood like cherry or apple.
Add the tri tip. Cook for about one hour, until it reaches an internal temperature (IT) of 125 degrees for rare or 135 degrees for medium rare.
Pull from smoker and rest for 15 minutes (or wrapped and stored in a small cooler with NO ice to keep warm if done early or needing to be kept warm before serving).
Slice against to grain, this is key for tri tip due to the way the grains change along the tri tip. Serve with your favorite sauce.