After seeing many posts that say "its done when its done", I tried something and it worked great.
Placing the largest part of the brisket in the center of the grill and using a thermometer to keep track of the meat temperature at around 187deg. I took a shish kabab skewer and put it into the vent hole. I tested the the firmness of the meat this way without having to open the door. The hole is big enough to allow you to poke the meat several times without hitting the same hole. This proved to be a great way to test the doneness of the meat in the event the thermometer was not reading correctly or if I had placed the probe in the wrong spot.
I now keep the skewer with the smoker.
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