I am going to wrap the entire cabin air tube and see if maybe that prevents the hose that is actually inside of the area from transferring heat to the tube as well. You may have already found this, but I figured that I would share just in case you had not.
This stuff looks like it could either fit over the tube or replace it. It also comes in 6 inch diameter. I dont know the diameter of theBroan at Lowe's: Flex Duct, 4", Insulated (25')
tube on our cars.