I need some music in the garage while i work on my car so it's not dead out there...

I have spare parts from car audio that i will use, so as u see, nothing in specific like building in the car...

I have a 10" sub Audiobahn Eternal wired to sundown 100.4 bridged at 8ohm.

Outputting only ~108w on a test tone is PLENTY of power for this 10" sub.

It can successfully drop down to 20hz on some custom music i made so i know it's not a bad driver to use for simple music setup.

Now, the box i have it in is not suitable.. but i have a problem...

The low end extension doesn't become really audible below ~30hz unless i am standing 20ft away from it.

How can I get decent low end output below 30hz while the enclosure is within 2-6ft from me?

It will be mounted underneath my work bench.

I have 7-10cuft GROSS to play with so i have plenty of room.

So what type of box should i be looking at to get better low end output below 30hz within a couple feet from the enclosure?

I was thinking of a T-line, never built one, but can they achieve this?

If you're considering a Transmission Line enclosure I suggest you read Martin King's work. There are different types of T-lines. Some are quite similar to a standard 4th order vented and others are not. Considering your space I think a standard 4th order vented would suit your goals just fine and I'm not sure at all if that AB sub is suited for a T-line. I think a larger enclosure would help out with low end extension and certainly be more efficient. You don't have the kind of cabin gain like you do in a car to help you out so things are different than car audio.

Here's a link to some useful information on T-lines Quarter Wavelength Loudspeaker Design