that cabinet would be fine but I wouldn't bother with the sand except in a 5gal bucket on the side. Making it air tight is also not necessary because you want the change in pressure to expand outward. The fire is usually very aggressive and very hot so it will consume oxygen very quickly. The trick is for the fire to consume the air in the space faster than fresh air can come back inside. This will snuff itself out for the most part and then your left with the hot copper foil sheets from each cell. Since the cabinet material is steel then I wouldnt worry about heat transfer as much. The Venom Stronghold charger and box I designed are made from duraluminum with a polycarbonate window. One box withstood multiple cycles without fail.