By the time you discover the water it may have gotten a chance to dry out on the exposed area. Look real close at the paneling under the windows for a faint but dry water stain/streak. Now I remember that leak doesn't usually go near the mattress if the window vent leaks. Look into the escape hatch by removing the inside trim. There are 4 screws to remove. Then feel the insulation with your hands. There should be more than just a faint amount of moisture if you do find the leak.
The escape hatch has a problematic area that is hard to seal because the strip pivot hinge is too close to the deck on the corners. Im currently having a new excape lid made of aluminum and providing my own hinges well away from where it needs the sealant to go up higher on the corners.