Well, you have three or four possibilities listed as the source, so far. That is the "magic" part of leakage, the result can be seen away from the source of the intrusion. Water will contact a frame piece or joint along the way and follow that to a spot where you wouldn't think there could be a leak. A pressure test is the best way of disclosing any leaks and, IMO, should be done when the TT is on it's way out the factory door. I don't know if any of the Mfg.'s do this but I'm guessing not many. There are a lot of spots where water can enter and a failure in any one spot can happen.
I would try to trace the water path from the nightstand area back to a wall, roof edge, or window. Carefully inspect those potential leakage areas on the outside of the TT. Heck, maybe recaulk those aeas as a peventative measure and see if that cures the problem. If the TT is still under waranty, I would bring it back to the dealer and demand a pressure test. Who knows, maybe the guy manning the caulk gun sneezed twice the day your TT was built.