I had rear fender liners put on my 05 F350 yesterday. They were not at all what I expected. I thought they would cover the entire inner fender area and protect the box. They turned out the be a little black plastic piece just above and behind the mup flaps. Might help a bit with stones etc. kicked back but they hardly seem worthwhile. I wonder if there is something made that would protect the whole area?
Also had the hood liner put in. It didn't significantly reduce engine noise as others had predicted. Was trying reduce noise to make my wife happier. Its not worthwhile doing either.