airspace for fiberglass box.

[lotz6996]

how do you measure airspace for a fiberglass box. im building one that will fit into the corner of my trunk. below is a pic, i need to put the other half on with the ring and get 1cu. ft. of air space for a sealed box for a hifonics zeus.
http://img61.imageshack.us/img61/3986/sn850313.jpg (http://img61.imageshack.us/i/sn850313.jpg/)
and the white stuff was a mistake but is fixed now, this is an old pic. its a lot thicker now than it was in the pic.

[kmanian]

build it as big as you can and get the look you are going for, then measure it after it is done (I use packing peanuts). then you can take space up with fill material to get the size back down (foam blocks).