What is between the sheetmetal and the inner plastic facia of the rear hatch? Is there room for a subwoofer there? Assuming you don't bang it to death closing the hatch, wouldn't it make a good acoustic enclosure?
I like thei idea of not losing use of the "wayback" just to have good sounds. I would like the good sonuds on a trip, when the back would be full. I also would like to not lose the cubbyhole on the left side. SO the hatch cavity looks promising. It would have to be mounted with some rubber or other softening material to not bang it to death, and as yuo say, rattles would probably have to be eliminated with foam or foam tape.
Anyone have a photo or manual diagram of the area under the facia? I was thinking two small subs (one on each side) might pack the punch and be relatively easy to install and care for.