I just received two smokers from a friend who was moving to Texas and couldn't take them on the trailer. He gave me a vertical water smoker of unknown manufacturer and an offset cheapo from Char-Broiler. I took the last two weekends to do mods on both. The vertical did OK, but It still is hard to control the airflow even after sealing it. It also is harder to keep up temps. More work to do.
The offset got the usual mods of tuning plates, large charcoal basket, large brick heatsink, and baffle. I also sealed the side firedoor to keep cold air out with a welded door jam. I also sealed the stack, but did not make the extension on the inside, as it already is only four inches off the grate. The mods worked great during seasoning, keeping the temps at 250 on both sides always within 10 degrees, usually within 5 or less, with adjusting the fire or stoking it three times for six hours once the temp was set.
For my other smoking hobby, I build model trains that are fired with coal. They are working steam locomotives that you can ride, and I machine every part, including the model valves. You can probably guess that I will always be a charcoal or stick smoker, as I like the challenge of playing with fire to get it right, versus the set-it-and-forget-it style.
Here is my diesel locomotive I built for the kids. It runs off a battery under the hood.