We also went through the same thing about 8 years ago!
A rock from and approaching truck shattered it. It was tempered all right, but NOT sandwich safety glass ... so it shattered in a million pieces and came down all around us while driving down the road. Why Winnebago didn't use both tempered AND safety glass is beyond me.
An auto glass shop in the Eastern U.S. replaced just the glass ... and it leaked in rain storms all the way across the U.S. back to CA. An RV repair shop put a complete frame & window assembly in from Winnebago that leaked again as received from Winnebago (rubber gasket to glass seal manufacturing defect). The RV repair shop installed another complete assembly from Winnebago - it hasn't leaked since. The repair shop scratched our Ford's hood when installing one of the assemblies.
Good luck with your repair. If we'd ordered our new Class C instead of taking an existing new one from the dealer's inventory ... we'd NEVER ordered it with a forward facing cabover window.
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2005 E450 Itasca 24V Class C