It's been three months since you first posted and you haven't had time to get it fixed???
Before you get more delamination and water intrusion, this really isn't a hard repair. Find out the right adhesive to use (Tiffin Service), clean the area really well, get your clamps ready, and go for it.
BTW, I had the same door delaminate on my Phaeton about a week after I sold it. No clue why it happened but the new owner got it fixed promptly at our local service shop that we share.
Roger & Mary
2017 Winnebago Navion 24V (Sold)
2014 Tiffin Phaeton 36GH (Sold)