There could be a lot of dirt and other garbage under there. My normally white bed was almost completely brown when I pulled mine off. Same thing, previous owner put it on and never touched it again.#2 - Pickup has a bedliner in it, I assume installed by PO. Car was outside and washed at least once by dealer. There are four openings for the tiedowns, in the liner. So.....I am assuming that I need to pull the liner and make sure that there is no water trapped underneath (rust). Am I correct? I tend to keep my vehicles a long time.
Depending on where you live, I would pull it off and make sure there is no rust under there. I got lucky, this truck has always been in New Mexico where rust is pretty rare. I would check soon.
As far as bedliner goes, I'm planning on installing monstaliner. Heard great things about it, and the price is not that bad