We were in the KOA at Nashville last year and had trouble with the fridge not cooling and the DT dealer next door (Bankston) wouldn't even listen to me about it, and only said to empty the fridge and it would cool just fine! Makes perfect sense!!
Not shocked you got the response you did about the leak. It should be fairly straight forward to isolate it from underside or maybe inside the basement sliding doors, check the dump valves for leaks.
One thing to consider (seen it happen) is if you were to have your black tank flush water hooked up and filling the black tank with the valve closed, it may have overfilled and leaked out the top of the tank below the toilet.
Also check the toilet to make sure it hasn't come loose at the base, take off the cover and check the bolts. This can also happen, and leak slowly into basement.
Hope it helps.
A dealer should look after you though, I'd contact DT and have them arrange it for you if you run into any trouble.
Cheers,
Bill