.13 Cu feet sealed enclosure: 6"-8" suggestions

.13 cu feet sealed enclosure (NOT including sub displacement)
mounting depth 5.5" (small shallow square 18.5x18.5x2" plus 8.5x7.5x4 square underneath (3/4 MDF materials) - designed to fit on top and inside the well of spare tire in old subaru legacy wagon)

-emphasis is sound quality
-mating with Morel Tempo passive 2way components +Aura 75wRMS amp and Kenwood Excelon X395 headunit.
-haven't picked the subwoofer amp yet.


Is there an SQ sub that will work in such a small enclosure? Suggestions? Can I add polyfil to artificially increase the cubic feet.

I have not modeled any yet in win isd. Some on my list include:

-JL 6W3V3-8
Eartquake SWS 8"
Alpine R8
Elemental designs 6.5 (if I can find one)
Pioneer ts-sw841d

Thanks.