My intention was also to just wire it into the left rear speaker

I wouldn't do that if I where you. I assume you have the overhead soundbar in your jeep right? Those speakers are so close to your ears that you don't want the amp gains very far up or you will blow your ear drums out and with the gains down you won't have enough power to drive the sub. If you really don't want to invest in another amp you might be able to get away with splitting the front outputs to all four speakers and then bridging the rears to drive the sub.

Anyway, as far as the sub goes I would try the JLAudio. I am pretty happy with the two JL 8's I have in the back of my jeep.

-Mike