Upon further calculations a 8" woofer would never hit below 40hz in that space with a sealed enclosure. Empire, looks like it will be an IB install after all..

i have some work cut out for me. Block off plates for 3 or 4 holes that would inhibit wave separation.

 

fiber glass the back, form molded... then use mdf front baffle,

 

It all just depends on what battle you want to fight really.
making an enclosure, you're going to have space issues. It looks like you have enough space to build a decent size box, especially if you build it out of fiberglass. But, small boxes don't always get really low frequency. So it would take some figuring and fiddling to get it right.
if you go IB, then you're going to have to get that sealed up and solid. You'll have to fight the resonance. Both of which, while they sound simple, can become a challenge real quick. You're more likely to get the sound you want from the IB set up, but it isn't going to be the "easy" way out, its just going to be a different set of challenges to over come.
For some, building a box and mounting it is easier. For others, proper deadening, sound control and sealing it all up is easier.


That's basically how I would see it working if you built a box.
Any other way and I see space being an issue, and build quality too since pretty much any other way would all but require you to build it in the car.

 

In case you haven't guessed this lol project has been shelved for a while. Other priorities came in to play(alarm w/ competent tilt/proximity sensors+ kill switches. Stealth install+ learning as I go is taking me a while) I figured of I'm going to add goodies I might as well protect tthem first. Pics when I get a chance.