Help With A Box

[kicker99chevy]

OK IV GOT 2 18 IN BTLS NOW IM MOVIN ONTO THE ENCLOSURE SPACE IS NOT MUCH OF A PROBLEM BUT I AM WONDERING HOW DO I GO ABOUT FINDING THE TOTAL CUBIC FOOT OF THE BOX BEFORE AN AFTER I BRACE THE INSIDE I KNOW ITS A BIT OF A NOOB QUESTION BUT IM NOT REALLY SURE AN WOULD LIKE TO KNOW BEFORE I GO CUTTING WOOD IF ANYBODY CAN HELP THAT WOULD BE GREAT

[Decaf]

1st, turn the caps off and id be glad to help

give me ur max dimensions the box could be, and power being used, and ur ultimate goal (spl, daily, low end monster)