I bought and started using a product called Plexus a couple years ago. It seems pretty good http://plexusplasticcleaner.com/about.html
, but by the time I got it, my sails were already 5 years old so it was too late to determine effectiveness.
As well, it doesn't have the hydrophobic properties that a product like Rain-X has. Enhancing longevity is one issue, but to me, visibility is probably more important. If there is a reasonable way to enhance visibility, or reducing labor restoring visibility, then it has some real value.
Opinions? Ideas? I have new windows and want to do it right from the start