I've tried to get wood chips to smoke on my propane grill twice, both time unsuccessful. Each time, i soaked the wood chips in water and then trained the water. The first time I placed them in an aluminum tray in the corner of the grill where the burner was off. The second time, I put them in an aluminum foil package, poked holes in the package and placed them directly over a flame. What am I doing wrong? Thanks.