OKay here's the deal. When you build a box you dont build it to fit the car only, you also need to build it to fit the speaker. There is more to building a box a certain size and dropping a woofer in it.
Your speaker comes with specifications, you need to use these numbers to design the enclosure, also the design and type of enclosure you build should be based on the type of music you listen too most often. I ALWAYS prefer sealed enclosures over vented or band pass, but thats just me. So start there, THEN you can make it fit the car.
Also check with the speaker builder, often they have already done all this research for you and have a specific enclosure design that works optimum with your driver.....
I have been building enclosures for many, many years (i'm getting old), I have probably built near 80 or so boxes, at least 20 of my own, the best one's are always the one's that are matched to the speaker, not to the car......
When it comes time to build it use nothing less then 5/8" thick MDF, assemble the box with liquid nails and wood screws. Space out the screws about 3-4" and pre drill all the holes. Use caulking on the inside corners, and you can line at least 3 sides with speaker insulation (available at radio shack for cheap!!). Interior bracing also may be required for some high power drivers and systems. Also when calculating the interior area of the box, dont forget to subtract the amount of airspace the woofer will displace when installed!! Meaning if they recommend 1.5 cu ft of air space for your woofer, that probably means you need 1.5 cu ft PLUS the speaker's volume.
Thats just my advice, I have seen all sorts of designs, materials, and exotic layouts, some of them work great, most of them are a waste of time and $$$. the more basic the design the better.
