That definitely looks like delamination. It indicates that water is getting in behind the fiberglass somehow. It's tough sometimes to figure out where it's getting in but that window would be the first thing I checked. Are the windows caulked properly? That happened to me on a 5er that I owned. No one told me that I should check the running lights for leaks. I resealed the roof every year but never checked them. I had to have the whole rear wall replaced. The insurance paid for the lions share of it so I let them do it. If I had to pay I probably would have torn it all down to the back of the fiberglass and replaced it all the best I could by myself. I'm sorry that you are going through this. It can be frustrating. Good luck.
