I have a 2011 RW 30C with a fair bit of delam at the back sides and front end. i have determined the source and hopefully stopped any further delam. I believe the primary cause was the plastic insert placed along the drip rail to hide the screws. This thing lets water and dirt get in behind it but, won't let it out. When I pulled it off, there was dirt and moss growing behind it. When I pulled the drip rail off and looked behind the rubber roofing, there were high water/rust marks about 2" above the screws holding the rail on. There was no caulking or sealant of any kind on the screws and they wer mostly installed at an angle like perhaps a left handed installer might do. This left a little gap between the screws and the drip rail that water could migrate behind and created the problem. That is my theory . I have fixed/resealed all that and will likely live with the delam knowing that it will not get worse. I got the rig for several thousand $ less than market for this model so, I don't really care about the looks. I love the floorplan and utility of the toyhauler. The interior was at least a 9 out of ten and everything works as it should.
To repair this involves opening up th wall and regluing the layers with epoxy. There are youtube videos of this process if you want to see what is involved. I have also talked with a dealer/repair facility that told me that Heartland had serious delam issues in several models from about 2010 until about 2016 that they had to repair. It would seem that the quality control in those years was almost non-existant.
Water intrusion was the cause, you need the location where the water got in. The water intrusion needs to be fixed. To repair the delamination issue, you will need to cut out that section and replace with new.