Two custom-built fiberglass 10" sub enclosures for sides of the trunk (similar to 4080 enclosures) with two 10" Alpine SWR-1042D subwoofers. Approximately $800 in parts, materials and labor.
Subwoofers have slight cosmetic damage from cargo prior to grill installations but does not affect performance.

Very old pics of the setup are available here:
https://www.rx8club.com/rx-8-multime...3/#post2812685

Asking $300 and throwing in electronics cover for trunk well (if wanted).

Please Email or PM if interested, I will not be checking forums regularly.