I have a COS and I have done some reading on mods to it for better heat control and more even cooking I should add some bricks to the cooking chamber to help hold the heat. Where can I get these kind of bricks around metro Detroit / Ann Arbor? Are they available at Home Depot or Lowes? Is lava rock an acceptable substitute? I know Wal-mart sells grill stones like a lava rock and they are pretty cheap?