I have done them three different ways on my Egg. Even though I mention searing in all three methods, sometimes they don't need the sear.
Cooking Method 1 – Set up the cooker for grilling with a direct set up and a grate temperature around 375°. Oak is the traditional wood for grilling tri-tip. Cook the roast for 15 or 20 minutes, turn and cook until the internal temperature is 125° to 135°. Remove and rest the roast while ramping up the cooker to searing temperatures. Return it for the sear, turning often. Rest it for 10 minutes and slice.
Cooking Method 2 – Set up the cooker for an indirect cook with barbecue temperatures around 250°. Oak or pecan are good choices for wood. Cook until the internal temperature is 125° to 135°, remove and rest while ramping up the cooker for searing. Return it for the sear, turning often. Rest it for 10 minutes and slice.
Cooking Method 3 - Season the roast. Put the roast in a zipper bag or a vacuum bag and submerge in 100° water for about an hour and a half. Meanwhile, set up the cooker for a direct cook using a grate temperature about 350°. Remove the roast from the bag, add more seasoning if needed. Grill the roast until the internal temperature is 125°. This will happen much quicker that when using Cooking Method 1 because the internal temperature of the roast will be 85° or higher when it hits the grill. Remove when the desired temperature is reached. Ramp up the cooker to searing temperatures while resting the roast. Return the roast for the sear, remove and rest a few minutes before slicing.