You shouldnt have any problem mounting the amp there as long as the seat can be moved forward and backward freely without scraping the amp. In my previous installations, when i have mounted under a seat, i have grounded to the studs which the seat bolts to on the floor. No chance of shocking anyone!
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ED7 --------------------- 20G Mark2A SN#: 010101680 1997 Chrysler Sebring LXi