I work on aircraft for a living and they tend to allow water to leak into them when unpressurised. This has much to to with the fact that they are built to slightly bend in response to turbulence. Most of this leaking occurs arount the rivets that hold the skin on and the structure together. As such, the engineers will definitely have some work on their hands trying to seal thousands of rivets per aircraft. This could translate to millions of rivets for the entire project adding to the overall cost. I love the idea though and wish they would build it in my town.