Cooking a good brisket is difficult on a kamado type pit. Even with using a pizza stone and a couple layers of foil beneath the cooking grid, it still burns the brisket up from the bottom because you have to leave it on so long, 10 - 18 hours. I finally found the answer; put a pizza stone and two layers of foil below, then suspend an extra grid above the cooking grid on top of two fire bricks, with a foil pan of water beneath the brisket. Finally got a great brisket; melts in your mouth!
To clarify; from the bottom up: charcoal fire, about 4"up the pizza stone and foil, about 6" above that the cooking grid, about 4" above that the brisket with a foil pan of water beneath it. Be sure the water pan does not run dry. Good luck!
Oh, and the pan of water helps to stabilize the cooking temperature at about 240 deg. Much harder to stabilize temperature without it.