The S-IVB stage would be a'wet workshop' similar to Skylab; the interior of the fuel tanks would be filled with living quarters and various equipment that did not take up a significant amount of room.
The S-IVB stage would be a'wet workshop' similar to Skylab. The interior of the fuel tanks would be filled with living quarters. The interior of the fuel tanks would be filled with various equipment. This various equipment did not take up a significant amount of room.