My car was already wired up for a sub (sub was taken out as well as amp pre purchase) so I've been thinking about putting one in. Issue is I want my trunk space and my spare tire. Only option I think that would work is what another user here posted in an old for sale item, an enclosure in the rear trunk left hand side empty space:
Not sure where I'd put the amp, also I have no idea how to build an enclosure. Want to avoid rattling the car. I don't need crazy bass, just enough to give me a decent bottom end. Not sure where else I can put a sub(s). Any ideas?

Not sure where I'd put the amp, also I have no idea how to build an enclosure. Want to avoid rattling the car. I don't need crazy bass, just enough to give me a decent bottom end. Not sure where else I can put a sub(s). Any ideas?