Sand Levels

Honestly an empty pan works just as good as one full of sand. The only time I add thermal mass to the pan is when the ambient outdoor temp is at of below freezing. the thermal mass helps keep the pit temp up when opening the door during the cold weather. Otherwise I leave the water pan empty lined with foil for easy clean up.

I used to fill my Smoke Vault-24 gasser pan about 1/2 full of pea-gravel...worked very well. I tried 4lbs in my WSM-18, but it seemed like it might have been too much...sluggish response when adjustments were made, but then it did hold pretty steady temps.

After a couple months I opted to run dry with just a foil liner in the pan and the WSM still runs pretty steady temps.

If the mass of your smoker is a decent amount you may not see much benefit from added thermal mass in the water pan. I am an advocate of using little to no water, though, but with a foil liner in the pan for drippings, so they don't scorch and make your meat taste like it's roasted.

Eric