"I called the dealer and was told that they probably overfilled the tanks during the PDI, and that if I jacked it up the water would drain out by itself"
That is a ridiculous statement. If water got into the underbelly from them overfilling any of the tanks, there is something wrong with the plumbing.
Don't accept that bogus "explanation".
If your state has a 'lemon law', I would demand a refund, and only repurchace the unit if there is no damage, and AFTER they fix the problem.