We've had windows done by an auto glass place that specializes in RVs. There was another option of a window glass place that could order my window from Winnebago to be shipped and then have an RV repair shop install it.
Based on our experience, apparently foggy dual pane windows may be able to be removed, cleaned up and replaced....or not. We had one done like that. The other had to have new glass because the water inside the panes had already crystalized and scratched the window panes (or something like that). Kind of imperceptible to me, but that's what they said. Same company that did the first window, so I believed them.