Great ideaRainX went on my shower glass and mirrors only.
I prepped my windows with a simple wash, glass cleaner, clayed, glass cleaner again then applied G3.
I've had G3 on 1 of the panels on my shower screen for a month now, prepped as above, as our area has terribly hard water and is still working well
Wash with pH neutral. Clay. Wash again and dry. Polish with glass polish. IPA wipe down to remove oils. Then your chosen sealant. The IPA wipe down could mean the difference between 10,000 miles and 30,000.
Having said that, the GTechniq system seems to work very well together. Worth getting the polish and sealant together, and forget the IPA if you go down that route.