PRAY....
Really, there is no realy means of making it water tight. It is kinda a cheap flimsy plastic cover that always starts to warp from the heat. Also, if you hit water really hard when entering, usually it gets sucked right down the air intake for the belt area....
Sry, but i really cant think of anyway to make it better with the exception of removing the cover and sealing it all up with a GOOD silicone, otherwise, it just suks...one thing i did do to mine was drill a small hole in the bottom of the cover to let the water out, this way when you finally get pulled out you can get going again without much hassle....
PS, trailblazers have the same problem
FreaAk