+1 on the snake method.
A 2x2 snake, started with a dozen or so coals works fine. Place your wood on top of your 2x2. You'll keep steady low and slow temps with minimal adjustments for 4-5 hours; you'll get more if you make the snake longer than 1/2 the circle. This gets tricky with whole packer because indirect space will get limited. I do mine on a 26 like JEBIV with a snake, and the extra real estate for a whole packer is great. To make life easier, once (and if) you wrap after the bark sets and you have the color you want, it's easier to finish it in the oven. You won't need smoke anymore and you can ramp up temps faster if you need to hurry. Plus, no more adding coals. I cook a lot of whole packers and I have some simple rules. 1) buy the best brisket you can find. Buy choice or better. Costco has prime for $3.39/lb in my area. Buy a packer, not a flat. Flats are difficult for the best cooks to keep from drying out. 2) keep you seasoning simple. SPG is perfect. 3) Do not cook it to temp. I usually go to 203 but you have to cook to tenderness. Use your thermo probe to check. 4) rest it.