Not sure if this is low & slow or high heat:
I've had good luck using a dry rub overnight (Big Bad Beef Rub (w/ added ground Chipotle from Amazing Ribs.com or your choice) & my WSM with a heat diffuser. A foiled dry water pan would work, I suppose (I use a 1/4" plate with a 1" rim that is foiled). Minion Method with several chunks of Mesquite. About 2 layers of charcoal in the charcoal grate- Kingsford Blue. 1/2 chimney of Kingsford Blue. Vents wide open. The meat is put on the grill (straight out of the fridge) at the same time the charcoal is added from the chimney. Cook to an internal temp of 122*, remove meat from smoker, remove center section, let the coals rage, drop grill grate to the bottom & sear the tri-tip for several minutes on both sides. Remove the meat to a platter, loosely tent with tin foil for 15 minutes before carving. If you are lucky, it will be swollen and jiggly when you remove it after searing.
While the meat is resting... grill some corn on the cob.