i built a box back in my day for 2 rf 15s. i made the box using fiberboard, then used some kind of bondo to seal it. i thought fiberglass was cool so i put that over the subs. then i covered it all w/ some heavy duty carpet. the only things i would repeat from this experience was the board and carpet. i disregarded specs for the subs and the subs sounded shitty (maybe it was also because i had a pyramid amp
). i've since learned from my mistakes.
take p11gt's advice. from what i know, i know that he knows a lot more than me, and it seems most of us when it comes to this subject.