I have bought a 2004 Silverado and got a removeable liner which will fit the bed. I am told that the slight movement of the removeable liners will scratch the paint off the bed and will cause it to rust. Does it make sense to put a bed mat under the liner to protect the bed from movement? Will the 3/8" height of the mat cause a problem with fitting the liner? Is there a better way? Or is this a non-problem?