I really don't want to do anything on the sides because the tank is already going to be narrow at 12.5 inches. Hmm.. I wonder just how thin I could go with the clay before it would crack and be a problem? Right now I actually have clay on three side of the tank that I will be using and it is extremely heavy. Maybe I could do just a swipe of silicone and mash in coco fiber. That way the tank wouldn't weigh so much. But would it look like it was down in a tunnel?