Our windows have frames, so we'll rivet snaps in all four corners. But I've also seen Velcro straps that wrap around the underside of the window and the elastic bands that Ken mentioned. I would think that the elastic may be affected by the sun over time and lose it's elasticity...
I guess you could sew little triangular "pockets" at the bottom edge too...then snaps at the top...
In a pinch the "clips" will work too...but I would think that would be a temporary solution...I'd be afraid that the point pressure of them may break a Corning glass window.
Whatever you decide to do, post a picture when you're done!
Shari
