Nah. I actually had to have my rails cut out of the bed so that i could install the Bedrug and Undercover combo the way i wanted it. The rails make the install quicker but it's not required. It comes with hardware for mounting under the lip.
mines mounted with the rails...but i helped to install one using the clamp on method on a truck that was a base truck w/o the rails....the rails really make it alot easier but its fine the other way as well.