If you're going with the W3V3 class anyway why not get the stealthbox which will custom fit the side of the Mustang trunk?
It comes with a 13W3V3 Ford Mustang Coupe '10-Up - JL Audio
It's also carpet matched to the stock carpeting.
Because it's $700.00. I can get my sub, the two door speakers, & amp cheaper than buying the stealth box.