Has anyone tried installing two woofer in each cubbie area? I know most people tend to install on the right and not on the left since the spare goes there. I was just thinking on one for each side to save space and even go with two 8" woofers or two 10" and stay away from one 12".

 

A single 10" is plenty for the XJ. An 8" is best for ease of fit.
The driver-side panel has the fuel filler and some wiring harnesses behind it.
I save space by using a sealed box that is self powered. Ported boxes/cabinets are larger.

 

The driver's side is more difficult because of the gas tank fill tube, but nothing that someone skilled with fiberglass couldn't handle. Fiberglass is much more space-friendly than MDF. I haven't made my enclosure yet, but it will be extremely similar to this one (as described at http://www.naxja.org/forum/showthread.php?t=1089395):




There are also ways of doing subs inside a full-size spare or in place of one such as....

Just make sure your math/geometry is solid and that you're familiar with pi--getting the internal volume correct for the intended subwoofer is very important.

 

I got a used 10" shallow mount and built a box for the rt side cubby. Plenty of bass for old punk and rock. It is enough for me.