I mostly smoke whole briskets, so I'm not sure if this is good advise, but thought I'd help, as I've figured out a lot of ways to dry out a brisket, and only one that has delivered great results on the last 3 attempts. I start with the brisket whole and not wrapped. Bring it to room temp. Pat it dry. Apply my rub of choice liberally, and pop it into a shallow foil pan. I have been seeing better results with large briskets if I use my Ranch instead of my WSM, but haven't gone back to try my newly discovered winning technique on the WSM yet so it may work just fine there too. Grill temp to 225ish at the grate right next to the fattest part of the flat. When on the Ranch I use the IQ 110 to regulate temp. I can't remember the hours needed but I bring the brisket to the stall or 165 whichever appears to be first, then pull and wrap in butcher's paper. Then I return to the grill until it reaches 190 internal (careful to avoid any obvious fat marble with the meat probe). If the grill runs out of fuel before the brisket reaches 190 I'll finish in a 225 degree oven. In a variation of this that also worked well, I skipped the foil pan and butcher's paper til I hit the stall and then placed it into a foil pan and tented foil.
I would like to get to the point that I can skip all pans, wraps, and foils altogether as the finished product would have a better texture, and maybe even more smoke. I feel the steaming that occurs with the pans, and wraps really effects the bark, and burnt ends. That said, The best whole briskets I've made have been on the Ranch, in a shallow foil roasting pan.
They have all also been big box purchased briskets from Costco, or other national grocer's. I've seen where the big shot BBQ boys tout the Snake River briskets and such as they have marbling all the way through the brisket, and that is what makes them tasty, juicy, and great. Since I caught that video on Youtube I have not been out shopping for briskets. But they said what makes the Koby Briskets from Snake River better is the marbling throughout the meat that the big groceries don't have. I will be looking closely under the fat cap on the flat and throughout the point to see if there is a difference between what I saw on the youtube and what I see at Costco. I generally get all giddy when I find a great price on brisket, but have never really looked that closely at the marbling. I have not been able to bring myself to paying $120+ for a brisket. Maybe when I've mastered smoking the cheaper Costco one's I'll give it a try, when I'm sure I'm not going to screw it up!