If your roof had hail damage, you'd see hail damage on the sides of your camper too. He's trying to bilk you. It would have to be some pretty hellish hail, (the size of a baseball) to do damage to the WOOD on your roof, under the rubber! PLUS you most likely, 100% would have had your skylghts and plastic vents broken by he hail too! (I know, we had our plastic covers on the roof of one camper broken by hail (all of them were completely busted up)... but there was absolutely nothing noticeable about the roof, or the wood under the rubber on the roof.
What that guy is telling you is the most ridiculous thing I've ever heard! Tell him to take a hike and get that camper out of there!