I'M going to be helping build a box for a friend and he wants a fiberglass box for the corner of his nissan altima trunk and he will be using a 10" RF P2 and I wanted to know is how would I be able to measure how many cubic feet the box would be because its not just a regular square box

 

an oldschool way is to get a bunch of packing peanuts and fill your enclosure with them, take them out then measure what was in there. Kinda sucks that way considering the box is already made though...