Why reinvent the wheel?
JL Audio StealthBox
Order one, measure it, copy it, send it back for a refund minus shipping costs.

The internal volume of the box MUST match the amount
required for the subwoofer or all bets are off.

 

You're not gonna copy that box with flat pieces of MDF....just not gonna happen.

And in a sealed box you're not gonna mess up bad enough with the internal volume that it won't sound good. That's why subwoofer manufacturers give you a range of usually + or - 1 cubic foot of sealed volume requirements. now if you're looking for a ported box......that's a different story

 

Plus that Stealthbox is designed for that JL subwoofer, so it possibly won't match specs for another subwoofer.......assuming you don't use that particular subwoofer of course.....I wouldn't

 

Plus as the volume changes within the + or - one cubic foot,
the resonance point also changes. Its a science designing boxes
with the proper Q and figuring out internal volumes and port
diameters and lenghts, etc.