I've have a couple of Longitude awning arms off a 2016 375BHFS. One motor side arm and one non motor side arm. I imagine they probably fit other model 2016 units also.
Sure, getting the cover through warranty is the way to go. I know those covers are going to be fun keeping them on in a few years. Basically snap together plastic. I was shocked what carefree quoted me to buy one complete arm out right. I would think though you can get just the cover if needed.