Pat the roast dry with a paper towel and mix the roast seasoning together. Rub the seasoning on the roast and set aside while your smoker preheats to 200ºF for 15 minutes with the lid closed.
Smoke the roast for 90 minutes.
In the last 10-15 minutes of smoking, prepare the carrots, potatoes, and braising liquid. Place everything in a 13x9 disposable foil pan or Dutch oven. (You can put the foil pan on top of a sheet pan for easier handling.)
Push the veggies to the sides, creating a slight well so the bottom of the roast is submerged in the liquid.
Cover tightly with foil and place back in the smoker. Increase the temperature to 300ºF and cook for another 4 hours or until the internal temperature reaches 200ºF to 205ºF.
Let the pot roast rest, covered, for 15-20 minutes before slicing or shredding.
While resting, drain the juices into a pot over medium heat to reduce to a gravy. Mix the cornstarch and water together to make a slurry. Add to the pot and stir well until evenly incorporated. Continue cooking until the gravy thickens.
Remove any stems from the herbs and plate the vegetables and roast with gravy.