I don't know about the collapsing part. But apart from the structural integrity, yes, it is possible to have buoyancy with rigid bodies. Actually, you wouldn't even need the gas.

See [here][1]

Actually, I am currently looking for investment to make a proof of concept of this type of airship with a certain types of light weighted materials :)

I found the following condition for buoyancy of a vacuum sphere:

$[1 - (R_{inner}/R_{outer})^3] \rho_{material} < \rho_{air}$

where $R_{inner}$ and $R_{outer}$ are the inner and the outer radius of the sphere, respectivelly.

$R_{outer} - R_{inner} = $ thickness of the sphere wall

  [1]: http://en.wikipedia.org/wiki/Vacuum_airship