I just finished modifying my Masterbuilt extra wide smoker, I have to say it turned out pretty good. I went online to the Home Depot web site and bought a 4'x6' sheet of water heater insulation. Its the type that has the cloth like material on one side and the silver coating on the other. I used 3/16 diameter rivets to attach it to the smoker. The only thing I might have done different there is use washers so I had a larger surface area securing the insulation. After I secured the insulation I took aluminum tape, the kind you use on your ac duct work, and sealed all the edges as well as covered the rivets, blends in perfectly. I left the material long so it acted like a skirt to minimize the chances of the burner getting blown out by a gust of wind. I then took some felt gasket material, it came in a 58" roll, used 2 exactly, for the door seal. I left the door uncovered as I believe that it is already insulated.
I replaced the stock thermometer with a Tru-Temp thermometer that has a 4" probe. The thermometer already had a 1/4"-20 threaded back so it fit right in. The dial is larger, but it still looks good. I also bought a 12" cast iron skillet and it sits perfectly inside the original chip pan. I bought a stainless steel steam table pan that holds a whopping 8.3 quarts. I also made a sheet metal plate, 5"x5" with a break at 2", for my temperature probe to sit on. With the magnetic back it should sit nicely on the plate. I attached the plate after I installed the insulation to prevent it from heating up. Take a look at the pictures and let me know what you think.