Once they start to peel there is no hope. I even tried carefully trimming the peeling edges back to where they were still solidly attached. But they just started peeling again.
Contact Dutchmen support and see if replacement decals are still available. You can also try ebay. They have some also.
You may be able to remove the decals with a heat gun and plastic scraper if they are still fairly pliable. If they are too brittle, then a 3M Eraser wheel in a good drill will remove them fairly easily.