This post is more for the hardcore backyard smoker. I own a New Braunfels Black Diamond smoker and have had great results with it for about fifteen years or so. That being said, there are a few downfalls to this smoker, which can be overcome with a little elbow grease.
After several years, my smoker started to develop some rust, especially around the firebox. I did what most people would do. Gave it a quick sand and sprayed it with high temp paint. That lasted about a month before the rust started up again. The next step for me was take the thing apart and have it sandblasted and coated. I had the whole smoker coated with heat-coat, which is what high-end headers are coated with. I also had the legs coated with a baked on powder-coat. Before re-assembling the smoker I gave it a couple of coats with high-temp paint.
As I put it back together I took care of a couple other issues. I sealed the fire box to the cooking chamber with fire brick mortar to keep smoke from leaking out through the joints. I also used oven gasket to seal off all of the lids. I replaced the wooden handles and tubular brackets with thick steal brackets and spring handles, which I welded on. I did this all about four years ago and the performance has increased and I haven't seen a speck of rust.
Today I started working on more modifications. In order to hold the heat and keep it consistent and I lined the bottom of the cooking chamber with fire with firebrick. The next modifications will be extending the inside portion of the smoke stack closer to the grill (cooking surface) and installing a baffle from the fire box, to the cooking chamber. My goal is the direct the heat and the smoke under the cooking surface. I just started mocking up the baffle and hope to have it finished next week. I've attached some photos of the modifications thus far.
UPDATE: On the above two photos, you can see that since I my last post I have added a Horizon Convection Plate. This is a 1/4" thick plate of steel that has a series of holes which change to a larger size as the progress towards the end of the smoke chamber. This connects at the firebox opening and causes the smoke to go under the meat then rise up evenly. In order to achieve this I also had to add a sheet of aluminum (until I make a permanent fix out of sheet metal). In addition to this, I extended the smoke stack down towards the grill. This changes the draft and again, helps keep the smoke low at the level of the food.