I talked with 303 and they indicated that their windshield washer tablets (WWT) are safe to any part of the outside of the vehicle, including wax. It's the alcohol that you have to worry about. Apparently, methanol is a lot worse than isopropyl (rubbing) alcohol (IPA), so they recommend the following combinations for winter driving.
Of course, if your reservior has more or less volume, adjust accordingly.
Water IPA (any drug store) *303 WWT Protection to
1 Gal 16 oz 1.5 to 2 26F
1 Gal 32 oz 1.5 to 2 23F
1 Gal 48oz 1.5 to 2 7F
* Use 1 tablet per 1.5 to 3 quarts for optimum cleaning
Use 1 tablet per gallon (4 qt) for normal cleaning
I am going to give it a try, as it sounds less damaging than some of those antifreeze mixes out there.