In a very weak personal moment I bought a GWS Slo Stick to see what all the fuss was about and to get an idea of what the then currently acceptable yardstick was for performance and controllability. I was seriously disappointed in the results in stock form. I only flew it one flight before I added a thread to pull the wings together and up to form more dihedral.

Having said this there WAS some small amount molded into the wing. But if you formed flat wings from the foam board there would be ZERO dihedral. And for a rudder controlled model to roll into a turn it MUST have dihedral. The more dihedral the more the model will respond with roll from the yaw angle of a given rudder input.