^^^^ That one. it's probably much cheaper(i've never bought prefab, always made mine).
now for the fun part. it need to be no more than 1 ft tall. and no more than 3 ft (36 in) wide. then you need to unclip the seat-release-pull to get the box in. you pull down the clip part on the back of it and push it towards the cabin. if this description doesn't help, i will take pic's tonight.
oh and what subs are you running?
yi im thinkin bout buildin my own my buddies uncle does all that kinda stuff ill prb just tlk to him...n i got 2 alpine type r 12s with the alpine 1000w amp i love em had them in my cobalt n sold them with it so had to buy new ones