I used to try all sorts things in my MES30 it I was never satisfied with the amount of smoke or the duration between reloads, so I bought the A-MAZE-N smoke generator. It cost $22.00, and burns pellets or sawdust.
Load it, start a burn, and walk away. No additional heat source is necessary to keep the burn going, but even though the burn is small it throws plenty of smoke and lasts for hours and hours. Whether I use it by itself to cold smoke, or if I use it in addition to what's already in my smoker I'm real happy with it.