I just got done reading the two drawer build that was just started and I have to say this is pretty much the same concept. I was given a three drawer filing cabinet from work and thought this was the perfect structure. I plan on going the electric route using an electric converter from Cabela's (http://www.cabelas.com/smokers-accessories-smoker-electric-converter-5.shtml). I think the 1500 Watt element should be perfect for this build.
I plan on using the rails, but turning the top two drawers into doors and using hinges. The bottom drawer will be used for sliding out to refill wood chips without releasing too much smoke and heat from the top.
Now for the fun part. I have built a Sous Vide using a PID and SSR relay before and I was thinking about going that route, but thought the on and off relay might burn out the heat source too quick. So I began to research some more ideas and decided that I would go with a ramp controller (http://www.lightobject.com/JLD633-64-Setpoint-Ramp-Temperature-Controller-for-FURNACE-KILN-OVEN-P47.aspx). Ramp controller will bring the heat up to a point and continue to step through the programed instructions. It has spots for multiple probes, one for the internal temp and the other for the meat. I'll be able to set the controller to turn the internal temperature of the smoker when the meat reaches its point to keep warm.
As I continued to research this product, I came across someone who created software to easily program the controller using a serial port of a computer (http://www.temperaturecontrolwiki.com/anuncio-71991259-Set64rs-XMT63-Temperature-Controller-Software-Creat-UpLoad-Manage-Profiles-Arizona-Phoenix.html). The guy also sells the controllers, software, and other parts through ebay.
The biggest question I have is the thinness of the filing cabinet structure as was pointed out in the other thread. I figure the whole point of the electric heat source was to be able to leave it on so it stays at 220 degrees? Yes the walls are thin and probably wont keep heat in very well, but the electric element should be able to keep it hot enough, right? I know I could probably structurally build the outside of the cabinet a little thicker, but if I don't need to I would rather not.
Sorry for the long thoughts, I'm hoping to get some feedback before I begin real soon. I will post pictures of the project as I go along.