Get the harness here:
https://technicpnp.com/product/hifi-...ub-harnessloc/
Takes him a couple days to make it.
Subwoofer Model:
http://www.jlaudio.com/cs110tg-tw3-c...-systems-93302
Amplifier:
http://www.jlaudio.com/xd600-1v2-car...plifiers-98604
Also, you may want to consider this:
http://www.jlaudio.com/acs110lg-tw1-...-systems-93334
I'm not much for all-in-one units, but being that this is a JL Audio product and after seeing the specs, it's probably what I would've gone for had it been readily available to me. Not too sure about it's dimensions, though, so I would measure. It also will use the adjustment knob that's geared for volume and not gain.
I sourced my sub and amp locally. Just search around for the best price you can find. You don't have to use JL like I did. Just something high powered and high quality.