Carpet underlayment: Is it necessary?

I have completed removing my old carpet, cleaned and restored the floor pan and am ready to install my new carpet kit from Vintage. There was a hodge-podge of padding under the old carpet. Is carpet underlayment really necessary? I am considering using neoprene but I am wondering if it is overkill.
Any opinions would be most appreciated.

I think closed cell neopreme would really cut down on the noise and make the carpet fit better. The ice-dam poor man's Dynamat is another idea too. I'd put something but would not use carpet underlayment --- if it gets wet it will never dry.

USE DYNAMAT PLAIN. YOU CAN GET IT ONLINE LOOK DYNAMAT AND CHECK PRICES, CAN ALSO PLACE INSIDE DOORS

Wolfgang, thank you. For the noise abatement should I take it up the vertical surfaces/sides also?
Thanks again.

Thanks Michael.

Place it everywhere. The layer adds weight to pnls and cuts down on vibratory noise.
Picture holding a sheet of aluminum in your hand. Tap it in the center=very loud.
Now smear anything across the middle of the pnl, tar,spackle, peanut butter. Tap
the pnl in the same spot==totally different sound, deadened. It will also give your door that
"production car clunk" when closed.
Sorry for my opinion but choosing to spend money for the name dynamat over "icedam" is
kinda like paying twice as much for one bottled water over the next because it has a pretty bottle. The power of marketing=wow.

Makes perfect sense. Very helpful. thank you.

When I installed my carpet I did not use GLUE at all. This way if (when) it gets wet I can simply pull the carpet out and throw it on the grass and let it dry. I installed it with stainless screws and nice cone washers. You can't see them anyway. Even up the tank area and sides. All screwed in.

Is this what you're talking about? This kind of stuff, anyway?

http://www.amesresearch.com/roof_coatings.htm

Cory - NO its not paint on. It comes in a roll at Home depot and has sticky stuff on one side (after ya pull of paper). Unfortunately you have to buy a whole roll - enough for maybe 4-5 cars. (or use it on your house roof!)

http://www.atlasroofing.com/residential/wm.asp

Thanks, Wolfgang. I'll be looking for some of that stuff when I'm done with the de-hooptification project. Whaddya say I provide a little delicious and refreshing beverage and see what's what before Carlisle? Maybe a little shakedown cruise, too?