Why don't you take a look at JL audio stealth box. They are custom made for your stang and are awesome.
I love mine on my 2011 GT
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2012 Grabber Blue GT, 6sp, FRPP Aluminator, 75mm pulley, Lund tuned Roushcharger, Roush cai, ID1000, Kooks super street, Magnafllow Street Series Axleback, MGW shifter, Steeda comp springs, Dynotech driveshaft, Koni Sport, BMR LCA & UCA ,Whiteline Watts link, Whiteline swaybars, JPC linelock, Forgestar F14 on Michelin SS 275/35/20 and 315/35/20
JL audio speakers & amp, Audio control LC2i, Raamaudio Ensolite.