I would think that to do a proper repair which is going to look good, it needs to go to a professional shop which specializes in RVs, and replace that whole panel. The panel most likely stops at the roof, and under the front at a seam. It appears to me it has been hit enough to cause that split, and no amount of fiberglass or repair is really going to make it look good.
If looks don't matter, then eternabond, etc. will seal it up, and you may want to go that route and seal it to prevent further damage from water intrusion until you can get it properly fixed.