That's what I thought you were thinking with the 150, Greg. You may want to re-think that, unless you want your brisket well over 200 for a finish. Dropping the temp for a hold is great, but you have to do one of 2 things: either lower your target temp to allow for the carry-over cooking, once the 150 is triggered, or remove the brisket, wrap in foil, and place back in the smoker, once it has cooled down below 150. Btw, I recommend 140 for the hold temp because your goal is not to continue cooking, but to keep it at a food-safe temp, which is 140.
These boxes are so well-insulated, that when your brisket hits 195, and the 150 is triggered, it may be another hour or two until the box actually cools that much! I use the open-door method, as I'm never not home when something is in the smoker, especially at finishing time!