Below is a cobbled together series of posts about 
my experience.  After more time on the road, it 
is definitely quieter.  My GF agreed right away too.

This project is now complete.  I put some Peel 
and Seal in the passenger door on top of the Tite 
Seal product that I had put in there first.  That 
helped that door to be quieter on the "thump" 
test and when closing the door.  The door closing 
is nowhere near and quiet and solid sounding as 
on a "modern" car like my 2002 Golf, but it is a 
lot less like the sound of slamming the lid on a 
garbage can.  Much deeper sound and less sustain 
or "ringing" after it's closed.  It seems like 
most of the remaining rattly sound when closing 
comes from the top window frame's meeting with 
the van.  Sort of slaps and bounces there.

So then for a test drive.  I am not sure, but it 
seems a little quieter up front right from 
starting the engine and beginning to move.  It 
definitely sounds a little different.  I'll have 
to put some more time on it to see if this is a 
psychological effect or real.  It's not a great 
big change, but seems better based on one short 
drive.  The speakers do sound quite 
good.  Especially for $15.  Rich the original 
poster had some additional larger speakers in the 
front, and that would probably round out the 
sound.  The Bass is not great with these but mid 
and high sound very good to me.  I mostly listen 
to talking people radio shows and rarely turn 
music up very loud.  I do like it to sound good 
at moderate volume though.  Now my rear 
blaupunkts are not too happy, and I have set the 
fader way to the front so as not to blow those 
out right away.  I wonder if there is a speaker 
that would fit in the stock enclosure back there 
that would be more biased toward resolving the bass?

This was a good little project and I'm glad I did 
it.  Thanks to Rich for the tip on these bargain 
speakers which pushed me over the edge to actually get this done.

Edward

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I can now tell you the "Tite Seal" I bought does 
not work.  It is sold as window flashing.  I put 
it inside the passenger door and thumped on the 
outside of the door all over the place and didn't 
notice much difference from the driver's door 
with nothing in it.  Not much difference between 
the sound of closing the two doors either.  Then 
I got some Peel and Seal today and put that in 
the driver's door.  There is a definite dampening 
of the sound and lowering of the frequency of 
what I hear when thumping on that door, or 
closing the door.  I measured with my digital 
caliper (whose battery was near death) and got 
.73mm thickness for the Tite Seal and 1.3mm for 
the Peel and Seal.  There you go.  Maybe Tomorrow 
I'll get the speakers back in the door panels and 
the door panels back on and really test it out.
Edward

>Date: Saturday, October 16, 2010, 1:13 PM
>the new speakers into the housing using "automotive goop."  I'm now
>going to apply some "peel and seal" type stuff to the inside of the
>doors like people do when they are doing this front speaker
>project.  I found 2 products at Lowe's.  The actual Peel and Seal 6"
>x 25', and something called "Seal Tite" (or something very close to
>that) 4" x 25'.  I figured that smaller width would be easier to
>apply inside the door and hopefully will do as good of a job
>deadening the sound.  Quite a bit cheaper per square foot, but not as
>thick as peel and seal.

At 06:51 PM 4/29/2012, Jim Felder wrote:
>Alternative for lack of a better word�meaning an alternative to the
>expensive products made for the purpose, that I have to order and
>can't get more of if I run out.
>
>Over the years I have heard people refer to a peel and stick
>asphalt-based product they got at the home stores. I was poking around
>today and found various sizes of rolls of peel and stick flashing. I
>was not impressed with how thin it was.
>
>Is this what people are using? Is there another product I should be
>looking for? Is it just not worth it, and I should be ordering the
>real deal?
>
>Those with opinions, please share.
>
>Jim