I bet most of you have already had this epiphany!! But, I bought some Rain-X to put on the inside of my glass shower doors as I knew it will prevent the buildup they always get. I have done this for years in my home, etc. But once I got done spraying the shower I thought, "what the heck!" I'll try it on my windows to see if it reduces the condensation....Oh Yes, it sure does. Just spray it on and gently wipe with a soft rag or paper towel.
My parents did that in their Rv with a similar produce decades ago, likely a forerunner to Rain-X. Of course, it's magnificent on your car windshield too.