How can I mod the stock sub location in my 2006 350z to fit an 18’ sub

[I have a subwofer adiction]

This is a bit odd but I have an 18’ edge street sub I whant to mount in the stock sub location the boot is already taken up by 2 pioneer subs this is all of a 10.1 inch kenwood with 4 300w pioneer coax speakers with most of the amps in the compartment behind the seat

Edited April 15 by I have a subwofer adiction