You can go with 2 10's and still keep the stuff. Get a hold of Thomas for more advice, or 411 the number to "Ultimate Racing" in Toronto, as they did the setup before, sorry i do not have the number. Practical, but not that great looking.
I build boxes for mkivs that hold a single 10". It goes down into the factory sub location. I have also built a similar box that will house 2-8" subs also. The box runs about $350 and will maintain all the factory targa storage as well as all the spare tire goodies. I can get a little over 1 cubic foot of internal space and if you are wanting to see a picture of the box don't bother asking. If you need to see a picture of the box then you shouldn't be trying to buy one. Just build it yourself!
No seriously, if you absolutely need to have more information about any of the above mentioned boxes contact supraforum member "Park" he has the box with 2 JL Audio 8" subs. If you still need to speak to someone else email me privately.
San Antonio, Texas