Best inside fog stop chemical

[65comet]

Ok, in high humidity situations you can have the inside of your windows fog up. And the best solution is air circulation and lowering of the humidity. But my wife has a unique situation, she is a school bus driver. Tons of kids exhaling moisture, wet clothes from standing at the bus stop and a door constantly opening to let them on and off. So let's leave mechanical means out of the discussion and just talk about chemical applications.
I have put normal Rain-X on the inside of a car windshield before. Biggest mistake ever. Instead of occasional fogging it was constantly fogging. On another car I (got smarter this time) used Rain-X Anti-fog on just the passenger side of the windshield. But I saw no difference in the amount of fogging or in the speed it went away after starting the defrosters compared to the untreated drivers side. I have also tried foaming shaving cream applied and wiped off that showed no difference. Anyone use anything else with any success?