hmm...What to do?

Well as some of you may know I'm slowly, but surely building up my first audio system, in my first car.  I have a Panasonic 903u deck, a pair of 6.5 type r components in the door and kicker 5.25's in the rear shelf.  Now I'm left with building the deep bass.  I had a few thoughts on this but still am unsure what I want/need since I have had no previous experience.

I was thinking about 2 - 8inch subs and a 12, or I was thinking 2 - 12 inch.  I want some balance to my car and I thought maybe the 2 8's could provide some low bass, but the single twelve could hit the very low notes.  Or is it better to go with just 2 12's.  I have a very limited amount of space.

I'm looking for loudness, I do not need GREAT sq but I don't want anything sounding like crap.  What would you suggest?

How bout two fosgate 10"

http://thezeb.com/caraudio/rockfordfosgatesubs.html#he2

Would 10's be big enough to hit the low notes though?  I want speakers that can shake the car when needed, and if 10's can do that then I would defintally look into that.

I don't make alot of money fast, but I have no problem waiting and saving up if buying more expensive things is the way to go.

And I just measured my cars trunk area. 36inch x 13inch x 24 inch (w x h x d)  And I don't car if my box takes up every last space I got.

Well I have never made a box before so I probably couldn't build anything really special, What do you guys think about a box like this:

http:///.com/dll?ViewItem&item=3041909406&category=14945

Are these guysfull of it, or is that a really nice box.  I will have to do some re-measuring to see if 15inches tall can fit, I just took a quick look with a yard stick last time so maybe this box could fit. 

These are alot better than that ebay one...ebay one the two subs look like they are in the same camber...thats a nono.

http://thezeb.com/caraudio/subzone_universal_sub_boxes.html

Its under vented enclosures.