ED NOTE: I found a digital camera at the pawn shop today, and I couldn't help but taken it home a play around with it.
This was my first real smoker before I got my BGE. It is a New Braunfels Hondo. I have cooked many fine butts, ribs, chickens and turkeys. I finally got it where I liked it after some trial and error.
The first addition was a Brinkman temperature gauge in the middle of the lid. I usually find that it likes to run around 300 when the butts are cooking right. That may sound a little high, but it seems to work out right in this rig.
I found that things that were on the left side of the cooker usually burned on the outside so I put in this piece of 3/8 steel plate to block the infrared energy coming off the coals in the firebox. It did the trick.
Finally my last modification to this cooker was a strip of stove gasket around the lid. There was a lot of smoke and heat escaping from around the lid and I found that after this was in place I could shut the dampers down as completely as they will go on this unit, and it will hold a temperature for a longer time.
Since I got my large BGE and I have since mostly stopped using the Hondo, except for large quantities if ribs or butts, but my next experiment was to insulate the body of the cooker to further stop the heat loss from the interior. My goal was to have as little heat loss as possible as well as have as little outside air entering the cooking chamber as possible.