try one of these. We tries larger canvas units, it seems once the smoker is covered, there's a lot of moisture build up around the openings. Using the 3 x 3 allows one to use it more strategically. We drape it over the top (toward front) allowing the hinged area some breathing room. Also wrap X amount of bricks in foil. That really makes the biggest difference. We used 6 along bottom & sides.
http://store.cyberweld.com/panfelwelbla.html