Might want to put some kind of liner around that aluminum box. If the cables get just right and short out you could have an explosion or fire. At least insulate your wires somehow! Batteries take a beating in a boat and should be secured well. I use battery trays like Dutch was saying.
T. H. MARINE BH-31P-DP - T-H Marine Battery Tray 31 Series BH-31P-DP - Boaters Plus