Choosing new woofers and box type

[Cardboardcat15]

O.k., hopefully someone knowledgeable can chime in here.

Problem: I don't know which route I should go when choosing what kind of box to build once I get myself new woofers.

Restrictions: Money, but more importantly SPACE.

SO here's what I have now. I've got two of the newer model SR subs from RE (srX). They're the 15 inch version. 300 RMS D4's on an AP1500 @ 1 ohm in a sealed, prefab box. The box is 5/8 MDF with NO bracing, and I've had the box for well over a year. Each sub is seeing a little over 1.5CF after displacement. I know that I'm losing some sound from this shoddy box.

ANYWAY, my problem is this. I have very little space in my trunk for woofers (reason why I have a sealed box), and I don't know which route I should go. I can't dedicate the entire trunk to a box because there is literally no place else in the car for amps. I've experimented with torres' Box calc and there's no way I can get a ported box for 2 15's in my trunk. Now, once I start my classes up again, my job starts which means a paycheck. Because I've pretty much got everything done with my car in terms of electrical and whatnot, the next items on my list are

New Box

and

New woofers

This is where I need some advice. I have NO clue if I should do ported or sealed, and for that matter, which woofer would suit my needs better.

So I'm going to give as much info as possible right now that I can remember. Hopefully someone is willing to help me.

I have contemplated a few setups, so here are some that I thought might work. My original Idea was one level 4 15 in a ported box, but I wasn't sure if I'd get much louder. (I am using DC audio as an example, throw in any other similar class woofer in it's place)

2 level 3 15's in a similar sized box that I have now. (Sealed, Double baffle, braced & inside glassed etc. a little less than 2CF per chamber)

1 level 4 15 in a ported box, with anywhere from 3.5CF-4CF (depending on port displacement)

2 level 3 or 4 12's in a ported enclosure (about 2CF per chamber depending again on port displacement)

Now there are a lot of other combinations I have thought of like 3 12's or even 4 10's or 4 8's all in sealed applications, but those weren't thought through too well because they would require odd boxes to be built. Plus the more power needed or more woofers would mean more $$$ for equipment.

So my question is, to you all, what would you suggest I do? My goal is to be louder than my current setup, which shouldn't be too hard. I just don't know if I should sacrifice motor force over cone area or vice versa. Also, I have NEVER heard a properly built ported setup in my life, so I don't really know the difference between the sounds of the boxes. I love how sealed boxes sound, I like the punchy bass and wide range coverage, but since I have never heard a ported box, I don't know the difference. Also, I listen to stuff like All shall Perish, The Eagles, Led Zeppelin and other non bass music on occasion, so I don't know if ported is for me. (Reason for my sketchiness on going ported)

I would say I can't fit more than a 4.3 CF box through my trunk opening, depending on it's height. I have (Rough estimate with a tape measure) 32' wide, 26' deep and 14.5 high.

So what would you guys suggest? I'm open to all opinions as long as they're helpful. If I feel I need to add anything that would be vital to helping come to a decision, I'll post it up here. Thanks for everyone who helps!