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It does work pretty nicely. I started smoking spare ribs that way before I got more serious and bought my lil' GOSM.
I don't recommend foil near a fire, as it could burn up causing possible hazardous vapor exposure to your food. A small tin can, burned out and seasoned, works great for a smoke wood holder. Place the wood in the can and lay it on it's side if clearance between the rocks and cooking grate is an issue.