Home Sub project - 3 12" MTX 71212 subs

Hi guys. I finally found a website link with the spec on these. Anyhow, I was thinking of tossing them into a sealed arrangement box. I was going to do 2 in one chamber, dual opposed and have the third in a sealed 2nd chamber below and firing into the floor. I'm thinking of powering them with my crown xls 1500 amp bridged @ 1500 watts @ 4 ohms (these are 3 12 ohm subs). They're left over from my car audio days.

I'll probably be using these in my garage for music. Anyhow, any idea on how big of a box I should go on these? Here's the link:

http://archive.mtx.com/caraudio/archive/thunderSub71212.cfm

Here's some photos of the project. I'm almost done with it....