I dunno if the 98's have them, but my 96 has fold down rear seats. I mounted my amp on the back of the driver side rear seat and my cap on the very front of the trunk(behind my sub box). I got lots of trunk space too! I gota take some pics. I'm sold on Pioneer as well. It looks pretty good.

96 Mystique, 2.0L ATX, tinted windows Head unit: Premier DEH-840MP Front Speakers: Phoenix Gold 5x7's Rear Spreakers: Pioneer 6x8's Sub: 2 12" Pioneer Premier TS-W1240C's Amp: Pioneer GM-X922