Ever think of fiberglassing the inside of that box? I did mine to reduce the box from flexing and it worked wonders for the total volume. My box went up 10db, slamming at 154db in my trunk. I've got 2 RE Audio XXX12's in a sealed 4.5 cu.ft. box with two hifonics bxi 2010Ds on each sub. I'm running two blown tweets on each to get the ohms down where I need it. Had to replace my rear windshield about a week ago. However, I probably wouldn't port your box up,reverbs off a roof can cancel out some of the lower end bass notes. Your setup will kick ass when all is done. Otherwise, You'll go deaf if you don't consider this warning! (Power Supply - Bass Boom Bottom ) Hell, I'm doin my best to try!