Originally Posted by Steeb
So that's what the cooler's for in all of those 3-2-1 methods.
These guys have given you some good advice but I just want to clarify something for you here. The 321 method has nothing to do with brisket, that's a method for cooking ribs and there is no cooler employed with that method. The name comes from the technique of cooking the ribs for 3 hrs, wrapping them in foil and putting them back in the cooker for 2 hrs, then removing the foil and put them back in the cooker for one hour. Basically you're cooking for color first (unwrapped), then tenderness (wrapped) and then to tighten up the meat a bit and set the sauce or glaze if you're using them (unwrapped). There's lots of info on the site if you use the search function.
If I could add one piece of advice for the brisket cook, it would be to resist the urge to lift the lid unless you have to add fuel or check for doneness. If you keep taking the lid off, you're going to have a long miserable time trying to get that brisket to finish.
Good luck and don't hesitate to ask questions. You won't find a more helpful (and knowledgeable) bunch of bbq fanatics on the internet than these guys.