I'm not sure what space issues you guys are talking about...
left:
right:
the wheel wells are shaped differently but as far as something being "too" far in the way to build a fiberglass box... i've seen much worse.
Dalton,
If you do go the route of making one, buying the other (i'm a DIY guy so I'd just do both... I'm a big fan of quality control... I get to control it
) then you would have difference in the sound response of each sub given that each enclosure would be difference airspace... however, that's an easy fix.
the enclosure that bigger than the other, throw some items in there (excess wood material works great) to reduce the volume of the enclosure to match the other.
as for enclosure volume itself, i'd be surprised if you couldn't get at least 1 cube out of the passenger side of the car.