I am gonna ask the obvious question, how in the heck do you access the ATESSA bottle?
plus, further to what Neil was saying, they are NOT free to air subs (sony xplod dont make them), and there is no way there would be enough space in them boxes anyway. I would heartily recommend talking to your local stereo experts and getting some proper sizes for those sub boxes. It may just be a case of extending the faces out into the cargo area some more, but just remember that the size they give you (usually in m3 or litres) will not include the incursion of the speaker itself, or the volume taken up by the amp. Sounds like a lot of stuffing around, I know, but the difference in sound quality will amaze you.
double thumbs up for the effort you have gone to for a killer budget sound system though.