You need to find the T/S specs for the woofer[s] your using, and then custom tailor the box to those specs, and if youve never designed/built a box i wouldnt touch fiberglass. standard MDF is quite the challenge, but if you have any questions shoot me a PM, ive been doing this **** for about 6 years, and just finished the new box for the GP [although i learned an important lesson, then beer does mess up my lines when cutting]