Ideas for 3 15"s in my trunk??

Well, after reading the responces from my other post regarding fiberglass and 3 15" subs, I think i'm gonna play it safe and stay away from fiberglass because i'd hate to waste all that time and money, then the whole thing rattles too much. So, now I think i'm gonna make the whole thing out of MDF.. and maybe vinyl it?.

Here is the picture of the current set up..

That's what I have right now. So, now I need to add a 3rd 15, and a 3rd amp. Exactly like the 2 in there now, same model and brand.

I really would appreciate help and ideas. It's a 2001 PT Cruiser in the picture above. As you can see, 2 barely fit, so I can't line 3 in a row, because the trunk is not wide enough. The truck is exactly 41" wide.  I am going to be putting in 3 15" inch subs, and 4 amps. 3 of the amps i'd like to be seen.. the 4th doesn't matter. Could I have 2 subs facing up, and 1 facing towards the trunk?. Or maybe have 3 somewhat in a triangular look on a "wall" of MDF facing the trunk. Where should the subs face?. Does it matter if they face towards the trunk?. Or should they face up?. Based on the install in the pic, those subs facing up really kick, and sound VERY loud, to the point my hair actually moves from the bass. Can anyone please help me with some sort of idea?. Also, does each sub need to be chambered?. Or can it be just one big box being all the subs and amps are the same?.

As for the finish, like I said.. fiberrglassing is out of the question. Is applying vinyl fairly simple?. Or, if I bondo over the finished MDF project, could that be sanded down, primed, painted, then clear coated and still look like fiberglass?

I am at a total deadend, so I am hoping you guys can help me with ideas!

Thanks!!

i think you miss understood the other posts

its going to rattle wether you use fiberglass or MDF, the point of the other posts was to emphasize this fact

which is why you HAVE to use some kind of sound deadener (more=better)

each sub should have a different chamber

and depending on how you build the enclosure, fiberglass can actually be stronger and give you a higher SPL

I HAVE DONE A INSTALL IN A PT, THAT HAD 4-15", AND IT HAD 2- DOWN, AND 2-BACK

RUNNING COMMON AIR, 2 AND 2.  AND I PUT THE AMP RACK ON THE BACK OF THE SEAT SO THAT IT COULD BE SEEN WHEN YOU FOLD DOWN THE SEAT.  I KNOW IT SOUNDS CRAZZY, BUT IT LOOKED, AND SOUNDED PRETTY GOOD..