To be honest I had always a lot of thoughts about this how Rama would be filled with air.... I mean it spins, but how Ramas filled it with air? Central Sea was one of sources, but water wasn't possible there before whole Rama being filled with air. So my thinking was always, air enters in the center, goes in all directions, hits surface which is 750 km/h... so ~40% of speed of molecules... how much it "slows down" Rama? Would there be needed some additional force to spin it? How long it would take to "calm down", and build gradient of oxygen/air in Rama...
Always was thinking about writting some simulation for it, but it was always "someday" ;-)
Just assume that Ramans were "złote rączki" and everything simply clicks together. I mean, if they were capable to build such ships in the first place, it wouldn't be (and wasn't) a problem to fill these with capable environmental control systems and suitable drive.
In the other books characters are put into hibernation so they could travel at high speeds. Perhaps atmosphere was removed and only minimal breathing mixture was provided for the passengers.
By the way, I think SciFun had an episode on this channel about O'Neill cylinder
Always was thinking about writting some simulation for it, but it was always "someday" ;-)