Those Alpine power packs are nice. Huge improvement over head-unit power. I've used the KTP-445U (the Universal version) and had great success with it. Although, honestly, If you don't need a 2-ohm stable amp, you might want to consider the Kicker KEY180.4 instead. It's the same red-brick sized class-D amp as the power pack, but it also has a built-in, self-tuning DSP, which really improves sound quality (it automatically sets EQ for each speaker, gains and time-alignment - all automatically) - makes the vocals seem to come out of the windshield due to the time-alignment. Really cool little amp (45Wx4 RMS). It won't be as "plug and play" as the Alpine power pack that is made specifically for an Alpine head-unit, but will give better results.
You set a mic on the headrest, push a button and close the door (you stand outside the car) and the thing sends sounds to each speaker and tunes everything using the incluced mic. Kind of like how a home stereo does it with their auto-setup systems.
I am looking for the plug and play ease of installation. This one doesn't do the automatic setup, but it has a few nice features.
For the price ($165 shipped), the positive reviews, and the ease of installation it seems like a good deal.
I was recently given one of those Alpine PowerPack amps (the 445U), and I ended up installing it in the wife's car, and I am impressed. The mini form factor was a life-saver, as that car has nowhere to stash a normal sized amp up front. And the output was quite impressive as well. It easily handles all four of the new 5.25" coaxials (and 2 tweeters wired in parallel on front channels) I just installed.
There's no doubt the average Dodge LX could greatly benefit from a significant amount of sound deadening, but doing it right and making the end result look like nothing has been done can be a daunting task...it is for me anyway. What kind of 8" sub are you running? I would think 350w would be enough to make it sing...what's the enclosure situation for it?
If it's a free air 8" mounted in the rear deck like the factory setup, I can see that being light on bass. I think the only way I've seen that approach work is when a custom enclosure was fabricated for the sub and affixed to its underside beneath the deck surface.
I used some fat mat on the trunk and under the rear seat when I was installing the upgraded fuel system and it seemed to lessen road noise a bit.
I took a peak under the front carpet when I was installing the new head unit rear cam and noticed a good bit of insulation there already. The doors don't really have any sound deadening so that will probably be the next body panel that gets attention.
I purchased a single 8" with a compact non-ported enclosure (I use my trunk a lot and need the space).
Oddly enough the best placement for bass to reach the cabin seems to be the rear right side of the trunk. I tried putting it up against the back seat but it didn't seem to help any.
The amp is mounted vertical to the left of the latch assembly.
I'll get some pics once I'm back, currently out of pocket for a little while...
The bass is easier to hear with the engine off, which is making me think the exhaust tone is overpowering the low end tones...
if it's still no bueno with the added power pack I'll probably just deal with it. It seems I can't have the terrorizing exhaust note and a quiet cabin at the same time...