A buddy of mine wants me to build a box for him. He's going to be running 2 Audiopipe txxbd 12s on a apsm-1500 and I'm not sure what kind of box to use. Should the subs be firing forward? down? up? back? Port front? back? side? down? 4th order? He wants to still be able to hear the bass when he has the top down. More info on what type I box I should use will be appreciated. Thanks.