Hi jimpco,
Welcome to the Heartland Owners Forum.
Delamination is almost always caused by water intrusion which raises the question of whether there's a leak somewhere. If you have a large (50%) area that's delaminated, that suggests a significant leak.
2017s started showing up on dealer lots in early 2016, so your 2017 could have sat on the dealer lot for as long as a year before your purchase. Unfortunately, dealers may not do required maintenance checks for trailers on the lot. So it's possible that dealer neglect could be part of the problem. While the dealer will likely expect Heartland to cover the repairs under warranty, Heartland may push back if the trailer has been on the lot for a long time and expect the dealer to pay for cost of repair.
If the dealer is less than prompt and accommodating about getting the trailer fixed, you should call Heartland Customer Service at 877-262-8032 / 574-262-8030. Have your VIN # ready.
If you're not the first owner, warranty doesn't transfer, so there is no warranty coverage, regardless of trailer age. It'll be between you and the dealer to work out a satisfactory solution.