I'm gonna sound like a broken record but how often do you use both seats? If you have small kids the answer may be that you actually do use them but otherwise you can only really fit one person back there... so scrap the seat and put the sub where the seat was facing forward.

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2008 XLT 4x4 - GRABBER ORANGE - 4.0 V6 - 5 spd
PNW CREW