I have a new Remington 870 express that will serve primarily as an HD weapon.

I bought a Leapers tri-rail so I could mount a flashlight to the barrel.  The tri rail is taking the place of the factory-installed clamp that connects the barrel to the mag extension.

http://www.leapers.com/product_images/mounting-system/mnt-br005xl.jpg

The tri-rail is made out of a lightweight aluminum and while it won't gouge the barrel, I'm worried about it scratching the fragile finish on the barrel when it's taken on and off (it has to be removed every time I clean the gun).

Is there anything that I can line the inside of the mount with?  I saw in a prior thread that electric tape would probably melt or soften if it's against a hot barrel, but what about something else?  Gorilla tape?  A fabric?  Keep in mind, I'm not looking to wrap the barrel.  I think lining the inside of the rail (that comes in contact with the barrel and extension) would be better.

I've googled the  he!! out of this, but can't find anything.  I can't believe there isn't a solution...

Not that this'll make you feel any better, but I had a mount like that and it shook loose pretty quickly.  Luckily the shotgun's off to get refinished now.  You could maybe call Mesa Tactical and see what material they use to keep their products from scratching the receiver, but that's not as hot as the barrel.

The heat on the barrel is my main concern.  I called the manufacturer (Leapers), and they didn't have any good suggestions.  The engineer said that since it's cast in aluminum, it shouldn't scratch the barrel but it could rub the finish off.

I think I'm going to line the inside of the mount in Gorilla Tape.  It sticks like glue, and has a somewhat higher heat tolerance than regular tape.  

A liberal coating of Vagisil should take care of it.

I would start by getting another mount.