Nice build. I can sympathize with the easier to clean up part, but I had do a little research on the second part and figured I'd share with any future thread readers. Sand can't hold more heat per gram than water. In fact, it can hold less than one fifth as much heat per gram: http://www.engineeringtoolbox.com/sp...ity-d_391.html . It can be between 1.5 and 2 times as dense as water, so at best those cans hold 40% of the heat energy they would hold if they were full of water, which could be a reasonable tradeoff for the easy clean up. Water can generally hold more heat per gram than all "normal" materials.