Does anyone have any experience with the Undercover SE or Elite hard one-piece tilt-up tonneau cover? I am interested in changing out my defective BAK-FLIP MX4, but some of the reviews online say this Undercover bed cap style hard tonneau will move a little and begin scratching the outside of the bed where it overlays. Is this a known problem with the hard tonneaus? Does the polymer bed rail cap prevent this? Any experiences? Thank you.