Egg shell trailers can leak. A friend purchased a 17 foot Casita last November. It leaked a LOT. And when they leak, the water sits at the bottom of the tub. They brought it to someone local and they tried to fix the leak but could not because of the way they are constructed. They drove it back to the manufacturer in Texas and came home and it still leaked a lot! The manufacturer came and got it and kept it for over a month. It came back home and the good part is it is not leaking anymore.
The point is you cannot assume these egg shell trailers do not leak and when they do leak, the water does not go anywhere. It sits at the bottom of the bottom half of the shell.