New Avalanche midgate sub box, two 15" l7s... which way should they fire?

So I am building a new enclosure, I have "outgrown" the four 10s and want something that will shake things up. 
My current idea is  2 separate vented enclosures (built to the same specs) appox 5.75 cu ft of airspace and tuned to 32hz (possibly lower, still up in the air on that).  But with this idea the subs are wiring into the cabin, with the vents along the bottom of the enclosure.  I have had a lot of boxes in a lot of different vehicles and placement plays a huge role, firing the subs up or down, rear or front... all make it sound different.  So I was curious has anyone else done anything different than the forward facing subs?  how did it sound?

Basically, my truck is very seldom used to haul anything, i hate to get the damn thing dirty for that matter, so space is limited only by the bed dimensions. I have thought about doing a bandpass style box with the sub firing back into the bed and then the ports venting into the cabin as well.  I just know with a box of that style i am going to have to be very exacting in the construction or it will suck.

Oh, and I already have the subs, and the amps (old school ZR1000 ) so no use in bashing the choice.  I have 2 twelves a while back and i have been bass-chasing ever since without finding anything close.  This is my attempt at re-creating and one-upping that system.

I didn't have a midgate enclosure but I had a ported box with two 12"s in the bed facing towards the tailgate and had the midgate down. They sounded pretty good. Not a lot of distortion like you get from forward facing ones.

Thats about as close as I can get

it all depends how much you wan a do. theyve had set ups where the whole bed was like a clam shell. but 1st off id  try actually feeding those subs what theyre hungry for. that small 1000rms amp is  ot nearly big enough. those are 1000rms each sub. so they can be fed  up to 1500 each. id be lookin ata 2500watt amp myself. i havent even started my setup yet but i have 2, 12in icons 1250rms subs ill be running a 2k amp to them i could have gone bigger amp but i didnt have the money. but i use my bed so im building a midgate that folds down still.

Yeah youre right.  I have two ZR1000s but even still I could probably find a bigger amp that wasnt so damn power hungry.

I did end up going with subs and ports forward though.

No complaints thus far... she hits low!

From a sketch:


To a pile of precut/labled wood:


It took me most of a day to get all the pieces in place:


soldering the terminals:


Moment of truth:

literally the perfect dimensions I could have played with the depth but width and height are spot on.

She is thunderous:


Big 3 completed:


and the twins:


0 gauge from batter to distribution block, 2 gauge from distribution block to each  amp.  8 gauge from amp to subs.

This could change by the summer... I have already started thinking of other ways that I could have done the box that might be better. 

Damn my overactive mind.

I bet that thing pounds like crazy!

Makes your eyeballs wiggle 

WOW oldschool amps there. Nice build.