custom speaker box 4 bed

anyone know how 2 build a custom box 4 your bed? I want 2 put a port through my bed into my cab, but i dont want 2 just cut a big hole in it. how can i fill the gap between the cab and bed? i have 2 10s in truck boxes now but theres just not enuf room in my cab. im thinking of running either 4 12s or 2 15s!