XTexan, the cooler is just to hold at temp longer and is not necessary. It does help to let the brisket "rest" for at least 30min to help keep the juice in the meat when slicing. A good "learning" experience is to make a slice after you take it off the smoker, juice will pour out. Then try slicing it an hour later, much less juice lost.
FWIW - I put my brisket in a large alum pan and cover tightly with alum foil when the internal temp hits 160-170*, this helps it cook faster. Then when internal temp hits 200-205* I take it out of the smoker and let it rest, still in foil, for at least 1hr then take foil off top to let cool for 15-30min longer to make it eaiser to handle. Then I slice it up, put in plastic container, pour the juice from the alum pan over slices and put in fridge or freezer. I do it this way cause I have never had a brisket finish when I thought it would, one will take longer than thought and one will finish faster than I thought. I don't take a chance, I make it ahead of time and reheated brisket is just as good if not better than right off the smoker.
More info than you probably wanted so I won't charge extra :)