i think a stout IB with a long-throw sub and plenty of power can meet your goals if you are willing to build a 2" thick IB wall that totally seals off the trunk and rear deck. that means a multi-layer wall that starts below the rear deck (below the torsion bars) and extends down behind the rear seats. i think firing the sub up at the rear glass will perform better by loading the sub (like a hatchback). that means cutting out the rear deck middle and building a new frame and baffle that is supported independent of the rear deck (i.e. have sides off the floor and angles off the baffle across the rear seat opening). you'll have space for amps behind the rear seat on that vertical baffle.
my 2001 Accord sedan had an IB wall that ended up getting to 3" thick behind the rear seats but the rear deck was just deadened/sealed, not reinforced. I measured 12Hz cleanly from that IB wall, so don't get worried about low frequency performance like some think. my build log (link in sig) shows you the process in detail.
it's really easy to hit mechanical limits so typically higher Qts subs last longer.
