There is plenty of room back there. I am willing to bet you could make a nice box with plenty of air space if you went sealed. I don't have a mega cab but I have looked into it. I have the jl stealthbox in my quad and it is nice. Heres the link
JL Audio: Products
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2004.5-{Atlantic Blue},6" superlift w/37's, all the free mod's, K&N drop in, Superchips Flashpaq, Phantom 2 gauges...more to come,
