Bingo. Huge thanks.

https://www.amazon.com/RAINLEGS-CL13.../dp/B001SEQRCW

I didn't think they looked worth it at first. They actually go on fairly easily. But then to ride, they do protect the knee from rain. Problem solved. It depends how much rain there is vs. the effort to find them and put them on, but if it's coming down, these will ekep the rain off and leave the back of the pant leg and seat uncovered so it's all breathable. I ended up with pretty dry pants and little sweating from these things. They work and go on better than what they look like just by themselves.