I did my first one with Fabic(sp??) in Madison. After hauling all the coyotes, coon, rats, ….after a trapping season, I have done every truck since and my ATV racks. Regardless if you have a topper, I suggest doing it over the rail as stated above. Really saves a lot of abuse on the entire bed of the truck.
My Dad did the Rihno liner and it discolored after hauling mulch. Other than that, awesome stuff