Did you look at the link I posted? That area looks like this:
In the photo, I have cut out the foam and luan from the fiberglass.
I had a lot of disintegration of the foam so I replaced that section. You can see the crossection vertically in the middle of the photo.
I don't see any reason your foam would not be fine...its a brand new camper... so you could probably remove the window and get adhesive into that area using a piece of tubing on the end of the caulking gun.
Sikaflex is really thick and hard to get distributed. Get a couple deep throat clamps on it and clamp it up. I don't think it will be hard to fix.
fixing my delamination