port phase and combined chambers

Greetings.  I have an 03 Tahoe that just saw it's first audio competition over the last weekend.  On their Term Lab, I could only pull a sad 145.7db.  I didn't expect really high numbers, but I was not happy with what I pulled off.  This being said, my system was not complete at the time.  I was working with 1 JL audio 1000/1 and 4 Diamond D3 12's.  I now have my 2nd JL 1000 back (just a few days too late) and I will be returning my other 2 subs into play.  3 subs per amp again, instead of 4 on 1.  I feel that my numbers basically sucked.  It seems like I should have been about 2-3 db louder.  My subs and ports face up, and each sub is individually chambered.  I plan to build a new enclosure in hopes of getting higher numbers.   The questions:

1.  Should I go 90 degrees out of phase (maybe subs up, port(s) back)?

2.  Should my new enclosure house all six chambered together, or should they stay apart?

3.  If I do chamber all of them together, should the specified volume per sub be combined verbatim or should I "de-rate" some(ex. each sub needs 2 ft, should I do 12 ft, more, or less)?  If so, is there a specific formula?

4.  Are there any other thoughts on the subject?

All help and advice is welcomed and appreciated.  Thanks.

I'm sorry, I'm unfamiliar.  Can you be specific or lead me to pictures of a CRX style box?  I don't know that I have ever laid eyes on one.  Thanks.