Two 10's? One 15?

If it's for SQ, why do you want so much speaker?

I'd go with a single DVC 12 in a small, sealed box with a good mono amp. It won't take up a whole lot of space and should have plenty of grunt to go boom if you want. Otherwise a 15 inch sub is pretty big and isn't suited to the fast transitions of many bass tracks. It'll boom and play loud but they can get muddy when pushed. However, they will make noise effortlessly. Is it good noise? Not necessarily.

Your other option of dual 10 inch woofers, that's OK too but that is a good deal of lost space. The only thing more woofers is going to get you is louder. SQ will be tight with a 10 inch woofer but you really only need one.

I'd go with the single 12 because it's larger size means it'll handle more power than a 10 and it'll dig deep in the frequency range. Deeper than a 10 but since the cone is 3 inches smaller in diameter than a 15, it isn't as likely to break up under fast transitions and the extra low-end extension can make a difference in an SQ setup. Also, the larger displacement of a 12 would be better suited to an open environment of an SUV but the small sealed box (about .88 cu. ft.) will not use all your space and doesn't stick out as much.

The four 8 inch woofers though, that has a cool factor but to get performance close to what a 10 or 12 inch sub can get you will require some fancy configurations like an iso-baric band-pass box. They will also take up a good chunk of space. Thier frequency range is limited compared to the 10's and 12's and they will likely not be able to effectivly pressurize the cabin to get that low end grunt that people expect from a sub. Also, you'd have to wire they in an odd way to get a load that your amp could handle.

No, it makes sense. All I'm saying is that the room in your home is alot bigger than the intierior of a Montero. A 15 inch sub would probably over-power the space. Dual 10's would be too much too IMO. A single 12, DVC or not, would give you the authority and effortlessness (is that even a word?) that you enjoy in your home but it wouldn't be boomy or muddy. In a car, even if you shove that sub all the way in the back of that SUV, you will still be "sitting on top of it" so to speak. If it is set up right, you won't be able to localize it at all. However, distortion and other noises are easily localized.

If you want boom, you need capacity, displacement. If you want SQ, you still need displacement but too much can hurt the setup and results. You don't need to go big.

I have a single 12 inch sub in a regular cab F-150 and it is much more than I need. So I keep the settings down and I get a nice, flat response from it. If I turn it up though, it'll kick hard and it'll go boom like all the kiddies like. I had a 10 inch sub and that was also too much but the 12 inch sub digs deeper. For a mid-sized SUV like a Montero, a single 12 will be plenty for an SQ sub. If you want to be able to unleash your internal kid, then go with more so you can go boom effectivly. Just make sure your charging system is up to the task. Japanese rides are notorious for have a bare minimum charging system capable of supporting very little else beyond what came in the car, stock.

Otherwise, a single 12 inch sub with 400-600 watts will be plenty of punch, especially if you go with aftermarket speakers and an extrenal amp for the rest of the stereo. If not, you will still have plenty of sound from a single 12 and you won't loose more than 2 cubic feet of space in the back of the SUV.

is sq like tight bass and spl loud bass??

A single 12 is my preference for a SQ setup in a car.

However, dual 10's wouldnt be horrible either. They could be tuned to sound quite good and if you felt the need for more spirited listening, they would slam pretty good.

Not a fan of 15's in a car for anything other than SPL.