IMHO, tri-tip only needs salt and pepper........although I usually add some garlic pwdr to everything.
Cook it to the same temp you like your steaks(rare, med, well, etc). I like to smoke them at 225 until temp hits 155-160(we like med-well), wrap in foil and let rest for an hour.
Important thing is to slice as thin as possible against the grain.
Tri-tip has a great taste and is hard to mess up. Make some au jus to dip it in and it is great. One of our favorite cuts.