With that big of a box I would put somehting ingthere to take up some airspace, wether it be some wood, or some books or somethinf(j/k), just maybe somehting to take up some space. And I think to wire the subs inside out or whatever you just have to wire the positive wire to the negative spot and vica versa......
Alpine Head unit
(4) Four Infinity Kappa 5x7/6x8 Speakers
(2) JL Audio 12" W3 Series subwoofers
(1) Rockford Fosgate punch 500S Amplifier
And two black fuzzy seat covers to top it all off