Chipmunk damage to Chevy Truck

Here is a link to Pictures on Photobucket (hope it works) showing the damage that Chipmunks did to the Insulation Blanket on the outside of the Firewall of my 2500 HD Diesel Truck. They tore the plastic blanket & removed the insulation and put it into the bottom of the Air Intake for apparently their nest. I did not realize they were using it to make a nest there until I changed the Air Filter. In the meantime before I found this under the air filter & discovered the little buggers removing the insulation I trapped about 8 of them and removed them out into the deep woods.
I inquired from my dealer the price of the blanket & it is $318 Canadian, he wants to see the vehicle to see the cost of installation, that will be tomorrow.
Curious if anyone has this happen to them with that Insulation Blanket and how big a job to replace and is it really necessary and exactly what is it for....stop heat from engine to interior or keep Air Conditioning cooler or a noise barrier?
Any help is really appreciated.....Ernie Photobucket