I run an 8" Solo Baric sub that's old enough to drink. rated for like a billion watts and is all I've ever wanted in a subwoofer. give me epic bass, but without sacrificing all my storage. It's in the Liberty now, but started life in the MJ back in like 98? it's old for sure. I'm feeding it several hundred watts right now. the amp is a cheap mono amp so I doubt it's spitting out the 1000+ that it claims. meh. still works great.
buy quality, feed it all the power it can take, and you don't need dual 12s eating all your valuable storage space.
or, if you're just looking for a bit of oomph to the songs without sharing with the rest of the neighborhood, any ol' 8" woofer in a small box will make you smile. you don't need to spend a ton because the cab is ridiculously small. you'll feel it for sure. just don't buy any speaker made of paper. not even sure if that still is a thing in the aftermarket, but just in case.