I was told by a few people to take a look at Horizon Smoker website to pick up a tuning plate to help control the heat flow. I sent them an email just to get some general information about the products they sell. They never answered back.
I measured the inside of my smoker and it's 40 in from side to side. The tuning plate I think I need is http://www.horizonbbqsmokersstore.com/servlet/the-335/Convection-Plate--dsh--For/Detail
Of course since the dimension are shorter I just wanted to be sure.