Make sure the propane tank has no gas in it, then fill it with soapy water and let it sit for a few days or a couple of weeks. A propane tank will explode if the liquified gas in it expands from being heated until it overwhelms the pressure relief valve on the tank. Be careful emptying the tank, because propane released to the air also can be dangerous, although it will eventually dissipate. Then use a welding/cutting torch to cut off one end of the tank. Once you have it partly cut, you can drain the water while you finish removing the end cap.
Set the tank on a temporary brace or hang it from a hoist while you build legs of pipe or angle iron. Weld those into place, with braces between the legs and cross members like a saddle to hold the tank. Then weld the tank to the legs. Next cut a divider plate of sheet steel and weld it between the firebox and smoking chamber, leaving a gap at the bottom so heat and smoke from the firebox will go into the smoking chamber under the grate. Then mark a door on the smoker side, weld hinges to the top side, then cut the door section loose from the tank; the door may warp if you cut it out before you weld hinges. Weld a handle to the bottom of the door.
Add a smokestack with stovepipe for a wood-burning stove. It can be on the side of the tank or at one end; place it so air will flow through the fire pit, then the smoker area and out the stack. You can make a damper plate of steel rods and plate and place it in the smokestack to regulate air flow.
Build a grate by welding a ledge around the cooking chamber --- angle iron will work --- and then either install a grate or weld one of steel rods. Reinforcing bars make a good grate. Make the grate removable for cleaning.
Things You Will Need
- Welding equipment
- Propane tank
- Angle irons and other steel for parts
- Metal saw
- You can substitute an old water tank or even two rounded stock watering tanks for the propane tank. The secret is dividing the firebox and smoking chamber, with good flow of heat and smoke between them and over the meat being cooked.