Tested with a pressure washer? That might work. Then again if they can see inside the walls...
The proper way to leak test an RV is to pressurize it. I'm not sure how effective this test is with a hybrid, but I can't see why it wouldn't work.
Chances are you are stuck. I've seen shops and individuals do some very clever things with delamination. So long as you find and stop the source of the leak, there are all sorts of ways to deal with the walls. Do a search on rv.net for delamination repairs.