The wOOx is very, very small. You might be able to mount it to the underside of the dash in the passenger footwell (firing downward). In this location, it would sound decent.
As for trunk mounting, the wOOx would probably be just enough to fill out the low end in the very lacking factory system (but nothing more).
But, I think that its boom/$$$ is really low. Even a 10" mounted in a .5ft^3 (marginally larger than the wOOx) powered by a mono bass amp would absolutely blow it away and cost less too.
On the plus side, it is very easy to hook up, has tons of mounting options with the included hardware, and comes with all of the necessary wiring except a patch cable (it's also got speaker-level inputs for integration with the factory system). If the passenger footwell doesn't work, I'd probably mount it to the underside of the rear deck firing downward.
Oh yeah, the included wired remote with level, phase, and x-over frequency controls is a very nice touch. It's definately a great tool for tuning the wOOx to your tastes from the driver's seat instead of the trunk.
