The smoker is a 45 gallon galvanized drum. Top cut out and 4" hole in the bottom for the smoke transfer pipe. Simple lid of roofing tin, corrugated to let the draft through. Hessian sacking acts as a fly screen and draft damper. Simple rails to hang the food from. Smoke box is a 25 litre drum on its side with the transfer pipe let in tightly at the top on the closed end. The lid forms the door and I use the 1" and 2" caps to let in the air supply. Simply by rotating the lid and using whichever hole is needed. Draft always at the bottom. The smoke is generated by fine hardwood dust packed into a roasting tray and set smouldering. I currently use oak but beech is equally good.
Use fine dry dust to create a continuous slow smoulder. Avoid fast burning as this wastes dust and creates heat which you don't want.
Fill the tray with dust and compact down, leaving it ramped at one end where you will start the burn. Use a blow torch or hot coals to start an even burn removing any coals before loading the smoke box. with the dust and tray I currently use, it will smoke for 5-7 hours, weather dependant.
It is important to note that you don't need lots of smoke, a mere whiff will do. If you have lots you will be creating heat. The required smoke is very little as all you are doing is allowing a small amount to condense onto the food and be absorbed. This process is affected by the dehydrated state of the food, time and to some extent the temperature.
Hope this helps.