Excellent diagram of a proper tri tip slice!
My wife loves tri-tip, and living in the state where they were "invented" makes them easy to find. The nice thing about them is they are so tender and fast to smoke. A real low and slow still only takes 2 hours to perfection, so they can be put on right after work, and still have a reasonable time for dinner.
I don't marinade, but my favorite is using a light Jeff's rub and mesquite pellets on the AMNPS and the usual 250*. I go to an internal Temp of 140* which is a medium cook - the tenderness is still there, but it is not bleeding all over the plate.
Combine it with a no-boil Mac & Cheese and you are in dinner heaven...