Hey bro, hate to tell you this, but you just ran into a problem that plagues the audio industry and has no simple solution; the vert. There is no foolproof way to install in vert's to create solid sound and balance.
As for your questions, I didn't look up the specs on the Kenwood but am sure that it can cruise over the 600 watt mark pretty easily and more power. If you wanna leave the bass tube behind and you want bass and more bass in your limited area I would suggest a bandpass setup. This is a two or three chambered box with sub(s) firing into the second or middle chamber which is ported. Excellent for bass needs in a smaller area. My first system had nothing but a bandpass generic 8" and it hit harder than my buddies two pioneer 12"'s
For the Kenwood amp question, it is a good amp but I'm not sure what you wanted it for. If you were going to use it to push your doors then it would be pretty good, but for the sub, I would stay with the rockford amp.
To summarize, I would probably first try pushing more power through the bass tube(check your speaker specs for safety) and seeing if you achieve what you were looking for. If it doesnt do it try upgrading to the other box and see what happens.
You won't ever get your bass to hit as hard as a non-vert but you can usually get it halfway close.
Thanks for the info on the top cover rattling with the bass. Something to remember.
[This message has been edited by Power (edited 06-19-2001).]