Basshead seeking Subwoofer/Enclouse Advice

Hi All. New to the community, but have been reading as much as I can here. Thanks to all the contributors.

Now, I am planning out a system for my 02 Camry. While I've settled on the speakers and amp - Going with the HAT Imagines I61-2s all around, powered by a JL HD900/5. Crossover centered around 80Hz, 85 tops. This gives me 500 watts RMS to power the sub and should be plenty loud. SPL is a far and distant consideration, (900 watts should be easily more then my preferred listening level). Sound Quality is paramount, especially with respect to the low-low-end response. I am a basshead, pure and simple. I listen to a lot of dubstep, trance/techno, hip-hop, metal. So while I may be skimping on my speakers a bit* - due to not planning on keeping the car for too long - the subwoofer/enclosure needs to hit those lows.

With that in mind, I could use some advice as far as the subwoofer & enclosure go. A caveat. Space is a constraint (I snowboard and the opening into the cabin must stay open) - so my plan was to make or buy a custom-fitted sealed fiberglass box to go in the left side pocket of the trunk.

I have heard many good things about JL subs. Considering the power I have available, I was looking at either the 12w6v2 or the 10w7 (I'm aware both have higher rated RMS, but JL graphs point to the optimum power for both at about 500W).
As far as the enclosure goes, two options here. Make my own or have a local shop make me one, or buy a pre-fabbed one from Bassforms.com** (only read good things about them). While I would love to go the Bassforms route, the issue there is the 10" and the .98 cu ft volume constraints. Considering my need to hit the lows, a) 10" won't go as low, b) the 10w6v2 is too wimpy and c) box is too small for the 10w7. Concerning problem c, my current thought was - stuff the box with Polyfill, at about 1.4-1.5 lbs/cu ft.
The seemingly better option is to make or have someone make me a custom box that is larger volume with an opening to acomodate the 12w6v2, as I've read these will a) offer better sound quality over the w7, although not SPL, b) will hit lower frequencies more clearly***, and c) don't need as much juice.
The two options should be relatively close to each other in terms of overall price, give or take $100 or so. Added side benefit to getting/making my own enclosure (2nd option) is that I can specify the front to be made of MDF, which would allow me to mount the amp to it (this is a big plus for me!). And since the Imagines are responsive down to 50Hz, I could even consider sizing up to the 13w6v2. To be honest, the only reason I'm considering the 10w7 in the Bassform is that its all prefabbed and would make the install easier.

SO, dear DIYers, considering I'm a major basshead, I love my love of the bass and sub-bass frequencies, which of the above options would you recommend I persue? Any advice, thought and feedback would be greatly appreciated. Note that I am not married to using JL subs either - just heard they are awesome for SQ. But, if there is another company that doesn't have quite as much of a "brand-sticker price premium" attached to it, I would love to hear it.

Note also that while I understand 2x woofers would give me even better SQ properly enclosed and installed, the money & space constraint precludes this option.

Thanks so much!


* I am also doing some sound deadening to improve the quality of the speakers. SecondSkinAudio products in the front doors (Damplifer + Closed Cell Foam + MLV layers outer skin, Damplifier inner skin, 2x layers around speaker locations, sealing the gaping hole in the inner skin, plus that dandy rear-wave diffuser behind the mid-ranges), rear deck (Damp + CCF and/or MLV, depending on the space tolerence), and trunk (Damplifier Pro all around + thicker CCF + MLV)

** Can't link on the forums yet. Specs on the Bassform enclosure are: 10" opening, 8" mounting depth, sealed, all fiberglass, .98 cu feet volume.

*** I realize that all generalizations on web forums are bad to go by, so for the sake of argument, assume both subs are housed in well designed and well built enclosures.

**** Posting from work, so have to use this disclaimer:
"The views expressed here are mine and do not reflect the official opinion of my employer or the organization through which the Internet was accessed."