My 2005 Colorado has a drop in liner, which I used to remove every fall season when it got its pre-winter cleaning. As that truck is still in my family, the most I have ever seen is a little paint rubbed off near the back edge where it has shifted over time.
It definitely looks like metal shavings were somehow trapped under there for it to rust that quickly....the pictures he provided do not appear to have originated from under the paint.
And while I got my 2016 with the factory spray in liner, I ONLY did that because the drop in one available when I bought mine did not go over the front lip of the bed.
There is nothing wrong with the liner.... either there was something in the bed before they placed it in or more likely, the dragged the new liner across the shop floor where it picked up debris and never cleaned it prior to installation.
2005 5 cyl, Black on Black, 4 door
2016 Z71, Black, Long Box, 4 door
Last edited by Toughsox; 05-18-2017 at 10:03 PM.