Replacing exterior skin

[cat2cat]

I am installing a new skin over top of the old one as recommended by Airstream. I am wondering if I need to take out the window in order to have enough room to slide the new skin up under the above one. Also do I need to trim off some of the metal at the top of that new skin to make it fit.
See pics.

[a duncan]

It looks like you have all the rivets drilled out, curious why you wouldn't remove the old skin, use it as a pattern and reinstall the new skin in its place. It doesn't look like it goes far enough to get into the window area, but mine is way older so I don't have a good reference.
Aaron