I have the red Weber gas grill with the wood shelves, the predecessor to the Weber Genesis model. It has the "flavor bars", three long ones above the gas elements and six (I think) short ones atop that. Rather than buy a steel box or other gizmos to produce smoke, I simply use a 6" square of 1/2" expanded steel between the two levels of flavor bars. After the grill has preheated a bit I drop in some wood chips on top of that expanded steel; when they begin to smoke, the meat goes on. I vastly prefer to grill over coals with wood chips, but when time is short or when circumstances or weather otherwise dictate I use this method. Gives the food a nice hint of smokiness without fuss.