I'm a little unclear on the actual details. Did you buy it new in 2017 after it has sat on the dealer's lot for 3 years? Or did you buy it new in 2014 and it sat on a site/lot for 3 years, and now you've discovered the issue after towing it to New Mexico?
I would think you'll have lots of issues getting Keystone to correct what the shop says is a problem from the factory, after 5 years. Is the "shop" a Keystone dealer?
My immediate thought would be you need to do a thorough inspection for water intrusion in the area where the roof material is pulled away.