There is real no reason to, hydrogen and helium lift approximate the same. But yes, a vacuum lifts approximately 10% better than hydrogen. So whatever the str

There is real no reason to, hydrogen and helium lift approximate the same. But yes, a vacuum lifts approximately 10% better than hydrogen. So whatever the structure is, if filled with hydrogen or helium it'd work similar. If you have some sort of mesh holding in a vacuum it's hard to see it's average density being less than hydrogen or helium or even air at the end of the day. Point is, everything is possible now. A void wouldn't value add.