I admit from the start that I didn't read every word in this post. But, from what I have seen, it seems to me that you decided to build an MDF enclosure to house 4 MTX subs. It also seams that you
1. Didn't have the whole thing 100% planned out when you began.
2. Didn't know exactly how much structure the enclosure would have until posting here for advice.
If my assertions are correct, then I can only assume that you haven't taken any of the T/S Parameters into account when building the enclosure? Have you even calculated box volume, taking into consideration the required volume for these woofers to perform? If not, then I hope you understand the ramifications of this. The drivers will not perform well at all if the enclosure is not built to spec. Buidling fiberglass enclosures is extremely difficlut for this reason, especially ones of unique shape. If you haven't taken the woofers specs, T/S, into account, then you may want to do that before you spend all of your time and energy on an enclosure that could wind up with a host of issues and terrible sound and performances from these woofers. The end result could easily be 4 woofers that sound worse than 1 woofer in a proper enclosure.