,I had about a 6 cubic foot box in my trunk for 2 12" subs. I sold one sub and one of my amps powering the subs because things were ridiculous loud. I mean, hard to breathe loud, blurry vision, you can't light a lighter in the car the air pressure is so whack, smoke will vibrate in the air, setting off building security systems, car alarms, letting girls orgasm on your trunk......
So it took up the entire fucking trunk, and you could hear me like 3 miles away. You will want to reclaim your trunk space sooner or later, and you will settle on the fact that a single 10" or 12" will suit you fine.
If you care about losing your hearing. From bass its harder than what you might expect....
Hearing loss comes primarily from loud noises higher up in the frequency range. Aka so your banging along listening to nelly or whatever the hell is cool now and its 45hz non stop BOOM BOOM BOOM at say 143dB.....thats not too bad on your ears. Meanwhile if you throw in a component set backed with a nice amp and you have a component set that can get to 126dB loud while playing a bunch of high frequency shit (cymbals, guitars, etc), you will suffer from hearing loss much quicker.
Long story short, bass = ehh yeah it can make you deaf, but a high end component set and nice amp will make you deaf MUCH much faster.