Preheat your Yoder Smokers YS640 pellet grill to 300ºF, set up for indirect grilling.
Preheat a Lodge Logic 7 quart dutch oven over high heat. Add enough vegetable oil to cover the bottom the dutch oven. Season your roast with Cattleman’s Grill California Tri-tip Seasoning. When the oil is smoking hot, place the roast in the dutch oven. Sear to brown on all sides. Remove from the dutch oven and set aside. Deglaze the pan with about 1/2 - 1 cup red wine, scraping the bottom with a wooden spoon. Remove from the heat.
Combine the onions, carrots, celery, potatoes, mushrooms, garlic, rosemary, thyme and bay leaf in a bowl. Place a layer of the veggies in the bottom of the pan. Place the roast on top of the veggies, then fill in the dutch oven with the rest of the veggies. It should be filled nearly to the top.
Whisk together the remaining red wine and beef base. Pour the mixture over the veggies and roast. Top it off with water, to nearly cover the roast. Place a lid on the dutch oven and transfer to the cooker. After about two hours, flip the roast over to make sure it braises evenly. Continue cooking until the roast is nearly falling apart, about 1 more hour.
Remove the roast from the pot. Cover and set aside. Remove the veggies from the braising liquid, as well. Add enough water to the cornstarch to dissolve the powder. Place the dutch oven, containing only the braising liquid, on a burner and bring to a simmer. Whisk in the cornstarch slurry slowly until your gravy reaches your desired consistency.
Serve the roast over the veggies, smothered in gravy.