JL Audio 500/1 Amp & the JL12W6 would be good for the bass, plus using a single 12" would leave you more
space in the boot, and make construction of a false floor with access to the spare wheel easier. Also the JL 300/4
get my vote everytime mate, I had a nice Alpine V12 4 channel previously in my car, and was very pleased with the sound, but the 300/4 moved the sound quality up a fairly big notch.
If you bargain hunt and are careful, you may be able to pick the amps up cheaper on ebay, but I would personally buy the subwoofer brand new of possible. Then nice big n chunky power cable etc and maybe some dynamat for the
front doors and inside the boot/back seat and you will be kicking mate
The Kenwood amps are ok, but I wasn't that impressed with the Kenwood Mono Sub amp I had previously in my car
(rated at 1000watts r.m.s), I changed it to the supposedly lower power rated JL Audio 500/1 and was bowled over
by the difference in sheer grunt plus increase in the quality & control of the bass from the JL amp.
You know what you are doing bud, but if you need a helping hand just let me know :)