chevy extended cab custom box

i know enough to be dangerous here but i still have some unanswered questions. ive done enough research to decide the route im taking, i have 2 exile 12" woofers with a monoblock 1100 watt amp, sounds nice but i want to go louder, and under my rear seat. at first i was going to build a custom box for the 12's but after discusing my predicament with the local audio guys ive decided to put in 4 10's and scrap the 12's to get the sound i want. im going to push them with my exile amp which should have plenty of power and run them all at 1 ohm. heres a little more detail, i have a 99 extended cab silverado, which is only 3 door, im planning on using 4 10" JL audio woofers, and my 1100 watt exile amp. my goal is to keep the box under the rear seat but since im very limited for space i will most likely bring the box out a few inches and run an angle so the woofers are pitched at a 45 towards the top of the front window. so my question is whats the minimum airspace for each woofer in each cell, and should i go ported or not ported, maybe a flex port? im very open to suggestions and ideas maybe even a little critisism, thx for any input.

Ok so I figured out the cubic airspace needed should be 1 cubic foot to 1.25 and I should be able to get about .9 atlest. So my next question is should I put ports in? Or will .9 be sufficient.

Thank you, so do you think .9 will be enough in each cell, or do you have any other suggestions.