hello
when you bought your sub (if it was brand new) it should have came with a manual explaining how to make the perfect size box to get the best performance out of your sub. if you lost your manual or bought it second hand jump on the web and type into a search engine for example "fusion 12 inch enounter box diementions" excuse the spelling.
another suggestion was just make a box to sit nicely in your boot in a place of your desire. me personally am to lazy i bought a in box fusion.
cheers
I don't stay with my my wife for love, spite really, i won't leave her cause that'll make her happy!!