I've tried Rain-X on my Rx lenses, not for fog which was never a problem, but to prevent droplets from forming. It helped a bit, but destroyed the coating so I gave up. Now when it rains, I'll get rid of the glasses, and accept soft focus vision. I can't read signs, but can recognize anything I need to worry about.

I came to this approach after broadsiding a slate gray van that I mistook for shadow because of the glare of oncoming lights through rain spotted lenses.

I just hd a non coated set of glasses made and may give Rain-X another shot when it starts getting dark earlier.