I have wondered if such a thing could be designed for use in the upper atmosphere and dropped in from space. That would avoid the need to keep out the full atmosphere. But then so would pumping out the air as it gained altitude...
I like this thinking! Like dropping a beach ball into a swimming pool.
But if dropped into the upper atmosphere where there is little air pressure, it would sink until it got to an altitude where it's weight equaled the mass of the atmosphere it was displacing.