I used a clear shower curtain when my kids were small and we were at WDW. They are teens now. It worked great. I tied it to the back of the stroller and rolled it up on the sun shade so when we went into any attraction I would cover the stroller and tie it to the front wheels to hold it down. Storms pop up quickly in Florida. It worked great. They could see out of it and it kept the whole stroller dry.
It may sound weird but it worked great and was cheap. I used the same one for a number of trips.