Hi momreed,
If you don't want to cut into the coroplast, you'll have to remove the screws that hold it to the frame. The valves are usually close to the frame, so you may only have to drop one side. Use an impact wrench. In addition to being much easier and faster, you'll avoid shearing the head off the screw, which often happens when using a ratchet wrench with socket.
If you end up cutting, one approach is to cut 3 sides of a rectangle, with the closed side toward the front. Then when you put it back together, you can use Gorilla Tape to reseal.