The good news is that this window is protected by a thick fiberglass rock guard while we are towing -- the rock guard flips up when we set up camp, serving as a sunshade. So unless someone throws a rock at us while we are camped (always possible), or unless we are hit by a really big rock while towing that penetrates the rock guard, I think we are ok.
The original window got a small crack due to thermal stress (I think), which rapidly turned into a big crack. Not sure what kind of glass it was. But the window held together (aided by a lot of duct tape), till we got home.
