It would be nice if someone actually answered this question, (although the bass tube idea is pretty cool.) I'd love to know if any sort of decent sub will fit in the sub hole on my sedan.

04 G35s 6MT BS Aero Kit/Nav/Prem
Warning: Objects in Mirror Are Losing!

 

I know the JL 8IB series does fit, but the problem is they are discontinued so it's up to finding someone with stock or buying a used one.

2004 G35s 5AT DG/Graphite/Premium/Huper Optik Tint

 

When you say "Bass tube", do you mean that you ported your trunk? Did you calculate the port's length based on the trunk size?

 

No, I just had a plastic tube fabricated to let the sound pressure levels through since my entire trunk has been Dynomatted. Otherwise the bass would be completely muffled.