We got hit in my DW's Honda CRV 2 months ago. When we asked about Diminished Value we were told to give them appraisal for what our car was worth after the damage was fixed plus the appraisal of the same car without the prior damage and they would start a claim.
So, what I would do is just that, go to an RV Dealership and see what they say.
We live in a world where CarFax can really diminish the value of something and the Insurance Companies know this and a good company will work with you.
Good Luck