I love my WSM. But I found that the water pan was putting too much moisture into the cooking chamber. I'd end up with mushy bark. Hey! It happens. Instead of sand or terra cotta, use ceramic briquets (for a gas grill). I line the water pan with foil. Place in the briquets. ANother layer of foil on top and your ready to go. I use a small foil loaf pan in the cooker to add "some" moisture. Plus the foil pan is just throw away to clean.
Jim S. Granny's Gang Barbeque NEBS, KCBS, CBJ WSM (2x)