My Undercover does not allow any water in. My Bedrug stays dust free and dry at all times. The only time it gets dirty is when my wife uses it in spring to pick up flowers at the garden center, but the pedals and coco bean mulch vacuum up real nice if you do it right away. I drove to my brother's wedding with my suit coat back there in a pounding rain for 60 miles and everything was dry.
The only way to get water in there is to make a mistake like leaving it unlocked and parked in a rain storm with the wind on the back of the truck. A strong wind can flip it open, so it's important to keep it latched at all times.
Look in my gallery, I have a lot of pics of both.
