Several different factors are involved in window fogging.
1 - The moisture in your breath, sweat, and cooking/coffee must be cleared from the cabin. Just blowing wet air around is not the answer. Try to set up a natural flow of air from low to high by opening windows a bit, drawing wet air out and drier air into the cabin. If you are moving, crack the front center window and the two front side windows to draw outside air across the inside of the windshield. Also open the back cabin windows a crack to eliminate any moist air back there.
2 - While most soaps do have surface tension reducing components in them, the bath soap bars also have ingredients that are 'thicker' and will hold the surface tension ingredient in place longer than liquid soaps. Take a bar of good bath soap, lather it up and very thickly wipe it onto the windows. Then use a very dry cloth or paper towel or keenex to just wipe the streaks off. That coating will last longer than liquid applications. I , too, use Rain X, but the thick soap application is more resistant to fogging to my experience.
3 - Warm air holds more moisture and the cold temperature of the cabin glass precipitates moisture more than a warm glass. I have tried the 12V defroster fans in heavy fogging/cold situations and they barely keep a small hole open. However, if you turn on the Wallas and blow the Wallas' hot air onto the windows, they will fog less. The Wallas moisture from combustion is vented outside so it will not fog your interior, but portable propane heaters will fill the cabin with moisture from combustion.
So... summary would be to put on a coat, crack the windows, soap the windows, and blow hot air on the windows.
If you have a Honda i2000 genset aboard, get a portable room A/C unit and turn it on "Dehumidify" and your problem is solved!
John