there is someting called ensulite that does the same thing, it is a thin foam type material (looks just like the stock except its black and a little thicker)--its almost inpossible to find online.
and you use 3m spray to stick it on the metal, mat or plastic. you dont really need though on the doors. the mat should cover up all the holes if you cut large peices. I have some and it does a good job if you install it right
one note-attach it to the mat not the plastic barrier--lol--that way is sticks ten times better--and do not install inside the door panel as it will hold water and cause mold if it gets wet
if you want it let me here is the guys email
raam@raamaudio.com
his name is rick
heres the website
http://raamaudio.com/products.htm (ensolite)
he is in claifornia so the shipping may be a littel high--but he is a great guy to deal with very trustworthy and he takes paypal for customer protection
late
oh yeah cascade audio also makes a foam type material called gator or somthing like that