bogleric

I have placed a solid Tonneau cover on my truck and it works great. What I have noticed is the truck bed is not completely contained in the front. Under the side rail of the truck bed you can see light and a significant space is open all the way through. You can snake something of a decent size and it's that way on both sides. Clearly made that way. My problem is while driving in heavy rain it scoops in a significant amount of water. Has anyone found a way to fill that gap?