A quick tip if you find your coals rolling off. Take a piece of heavy duty aluminum foil and make a round ring around your bowl about 1 or 2 inches high which will keep the coals from falling. Actually this will even be a mini wind breaker if you want, you can make it even higher to hold the heat in better also. Don’t throw it out since you can re-use it as long as it retains its shape.
I had tried a¬† water drain cover, but it gets hot, and also I’ve read that galvanized steel is¬† dangerous tosmoke off. It did taste pretty bad.