You could have multiple membranes wrapping one another, each with a lower pressure than the last until vacuum. That way you substantially reduce pressure forces

You could have multiple membranes wrapping one another, each with a lower pressure than the last until vacuum. That way you substantially reduce pressure forces, and improve ballistic resistance. Make it big enough, and vaguely cylindrical, and you could spin it up to provide simulayed gravity - you'd just need internal webbing to prevent it bulging from centripetal forces. This all adds mass of course, but it still be lighter and more compact than an equivalent rigid structure.