Turning a cast-iron grill into a smoker
Any cooker with a lid that mostly closes the BBQ will work as a hot smoker. It doesn't have to be a perfect fit for hot smoking

Just add something that smokes with the radiant heat. Place it under the grill to the side, or on top of the grill if there is room. A crushed up bunch or tea tree or lavender twigs works fine. If the smoke runs out, add another bunch

Any wood will do, it doesn't need to be "fancy smoker chips" *. It doesn't need to be soaked or fiddled with in any way. Wood with nice smelling sap/oils seems to be better, but experience tends to indicate that any old wood will do

For temperature regulation, just concentrate on cooking correctly and safely. The smoke will do its magic regardless. You generally need more than ten minutes in smoke to make a decent impact, but for thin cuts or soft flesh fish you can do it in less


Referenced from Nathan Myhrvold talk promoting Modernist Cuisine