I've had an Undercover since Feb 06. It lives up to the advertising - watertight, easy to remove, lightweight, etc. I like being able to lock up my gear.
However, the box of my Titan is not square. This, combined with a fairly tight fit and contraction of the plastic in cool weather, causes contact between the bottom edge of the cover and the side of the truck box. It doesn't touch the box on a sunny 80 degree day.
If I had my time back, I would have gone with something that doesn't curve over the side of the box. Or, buy accessories from the dealer, and they have to fix the issues.