cause i had some boxes laying around and wanted some bump in my truck i should have my 2 18 test box in tomorrow and be charging at 18.4 im only doing 2 right now to figure out the proper air space for 4 of them before i build the monster box 2 layers of birch all around and a tripple top flush mount and 4x4 45ed for all corners and 2x4 for bracing