New enclosure recomendations

Alrite im getting rid of the 10's in the front center console and planning on putting some 15's in the back of my expy. I have plenty of room with the 3rd seat taken out. I just bought 2 15" M3's from memphis. I am planning on buying a 3rd one. I need some recomendations on how i should design this box. I was thinking about making a box in the shape of a half hexagon, and having one sub in the middle and 1 on each side facing in. I plan on slot vented all 3 subs. Also having an amp rack on the top for 2 amps. with some red LED's. Should i seperate each sub or have one huge enclosure for all 3 subs to share air space? Is this an ok idea as far as bass goes? I also plan on fiberglassing over the MDF. All suggestions would be helpful or any pictures to help me out that would be appreciated. Thankyou!!

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03 F150 on 24's
HU:Pioneer DVD5700
Frt:MC57
Subs:(12)S12L7
Amps:(3)KX2500.1's, MC-2004

This is "3 Subs Nite", so you're just in time.  Did you figure the impedance you'll be using with 3 subs?  Personally, I think you could get more db's and better quality sound using two subs firing in the same direction.  But the neon sounds good.

Alrite good. Im getting some feedback. I appreciate your reply stevdart. So u think i should just go with 2 15's facing the back? If i went with 2 15's i would wire them at 2 ohms. Andyone else have any input?? Thankyou

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03 F150 on 24's
HU:Pioneer DVD5700
Frt:MC57
Subs:(12)S12L7
Amps:(3)KX2500.1's, MC-2004