need advice on a sq 12 sub

Good morning all.  I'm trying to find a sub to fit my needs.  I'm looking for a single 12" sub to go in a small port enclosure.  This is going on the passenger side of the rear cargo area of my 84 Chevy S10 Blazer (please see the attached pic to get an idea) and the driver will be firing towards the driver side.  I'm not sure about port direction yet.  I have a 5 channel Memphis  16-MCH1300 to run it and the rest of my system.  I'm looking for a single one ohm or dual 2 ohm sub so that I can run the sub channel at 1 ohm and get the full 1100 watts RMS.   By my guestimation, I have between 1 - 1.25 cu ft to work with.  I would like to make a ported box with the proper tuning for the sub.  I don't want to put anything in my center cargo area as I drop the back seat and haul things from time to time.  I'm leaning towards FI Car Audio, but am not sure if they make a sub that will fit in that small of a box.  I'm also going more for sound quality and I listen to a wide range of music from classical to jazz to rap.  Price range is under $400. 

Any suggestions?  Thanks in advance.

Jason

Sorry.  The image didn't upload.  Let's try this again....

As previously state, it's going on the passenger side firing towards the driver side.  I plan to fiberglass the back of the enclosure to gain as much space as possible.  It will go up as high as the window sill and come out even with the finder well.  It will run from just behind the seat all the way to the tail gate.  I don't have exact measurements at the moment.  My goal is to wrap or cover it so it appears to blend with the interior rather than looking like an after thought. 

Thanks again for any and all advise.

Also, I just saw this post.....

https://www.the12volt.com/installbay/forum_posts.asp?tid=43055&KW=s10+blazer

but he is wanting a sealed enclosure whereas I'd rather go ported if I can.  Just wanted to put that out there before I get flamed lol.

Ok, fair enough.  I don't mind SPL, but it's not my main concern plus I do want to get the most from my amp.  I have a Dayton Audio 12" H.O. sub in about a 1.5-1.75 cu ft ported enclosure powered by a RF 100ix bridged mono and it sounds great.  The only issue is that it's only a 4 ohm sub and the Memphis will only do 300 rms at 4 ohm.  Plus it's not on the side of the cargo area where I want it.  I'm not apposed to a sealed enclosure, I'd just rather do ported.  I did my first properly tuned ported box and I've been spoiled I guess. 

I know you want to save space, but I don't see why you cant squeek another .8-1 cu.ft. and go ported. Just make the box a little taller and narrow.

I hear ya, my problem is that I like to cram in as many speakers/box as I can fit haha. Good luck!