I always keep two heavy duty contractor bags in my backpack along with two quart size zip lock bags. The first contractor bag goes on my lap and the second bag goes over my legs. Finally, the quart bag goes over my controller. You can easily add a few rubber bands to keep the zip lock bag on your controller.
With the right attitude and a little preparation a power wheelchair user does not have to call it quits just because of a little rain. Good luck this season, shoot straight and be safe.