I usually put them on when I'm smoking a brisket. Low and slow at about 225. The tomatoes will only take about 45 minutes to an hour to pick up the smoke. Typically you'll be using them in another recipe so you don't want to cook them too much. You'll need to find the hot spots on your smoker and adjust accordingly. Have fun with it! Edited: for wood you might want to stay with something milder. Pecan is good, but hickory or mesquite might be too harsh. Oak is mild enough.