need help with new box

[Gr1m]

so anyone i broke the seal on my last box because i guess i used 3/4" thick MDF and kinda rushed making it. what im looking to do this time is just use one of my HCCA 12.2 and hook both my 2400 amps up to it in a bigger box made with 1" MDF this time, and just sell off the second sub.

the current box i have in there right now is 17"x42"x7.5" and that is as big as the box can possibly go, but im switching from two subs to one and i cant seem to find the proper space i need for one of these subs to hit properly. they are orion HCCA 12.2 (the new 2009 models)

anyway the 2 fixed variables on the box are the height and depth, but i can change the width from 42" to anything smaller, i just need to find out the proper CU i need and change it.