no way to fit them behind your seat. You should be ok without capicitors, what amp are you running? I ran a 1000 watt alpine amp without a cap and was fine, no dimming of the head lights!
Im not sure about raising the seat, never seen anyone do anything like that so idk how it would look. but tank always knows so idk.
I saw a guy that had subs in his bed in a simple box, but he had a camper shell. not sure how it sounded tho.