I just finished installing one of the firewall pads sold on ebay by benzrestorer. The transaction was fine - he shipped promptly, and since I bought three, he combined the shipping.
The pad itself is stamped and mounted on a dense foam backing with peel-and-stick adhesive. About 5mm thick and quite stiff.
The fit was OK. I had to trim the top to get the large piece to fit against the seam at the top of the firewall, and take a little off the bottom to clear the wiring harness that runs across the firewall. I had to make my own hole for the AC dryer.
The adhesive is really sticky, very difficult to move when it even touches the firewall. So my technique to deal with this was to cut the paper backing so that I could do a section at a time. I made cuts so that I could do the top, left side, then right side separately. I started by peeling the top 2 inches off and putting the pad in position along the top seam. Then I reached under and peeled off the left side and pressed it into position, then repeated for the right side around the AC dryer bottle.
Appearance-wise, I was pleased. You can look at the picture and judge for yourselves.
Cheers,