I understand that it would be the "best" thing to clay everything, the issue is that I don't have enough clay, so what I finished out with is about 3 inches of clay for the bottom of the entire box, and the walls of my trench are made of clay they are about 2-3 inches thick, and the rest of the box is filled with sand, I am considering either packing bricks in the sand so that I wont have to fight the sand when I need to rake charcoal in or just making a top layer of clay which do yall think would be best?