John. If your Airstream was worth a few thousand then insurance companies would probably agree with you.
However, your trailer can be repaired properly, by a few dealers, as well as the factory. It won't be cheap, but it can be done.
Perhaps the best out for you is to have it repaired, and then trade it.
Houses flood all the time, but they are not totalled.
What caused the original problem? In my 36 years with Airstream and 4 years with their insurance division, I have never heard of a black water tank flooding the interior.Andy