Flood insurance on a house is far different than any other kind of insurance. I know, we have flood insurance on our house. It's a federal insurance, separate from your home owners, and subject to a bazillion rules. We filed a claim a few years ago (so we found out). Insurance on your trailer should cover. This would probably fall under the same category as a tree branch falling on your roof and putting a hole in it, although much more serious.
Water damage from a broken pipe may be on YOU for the repair. Water damage from a flooded river should fall under that same category as a tree branch.
Why not have the adjuster get a row boat and row out to the camper? Good luck entering the inside though!
Hey, for what it's worth ... that's a great photo! Thanks for sharing! Hope this works out ok for you too. (Keep a positive outlook, "this too shall pass!")