You might be interested in the story of Radio Caroline, back in the '60s the BBC had a state monopoly on British radio and it was very stuffy and conservative. To get around this people used to set up AM transmitters and studios on ships just outside of UK territorial waters and transmitted from beyond the jurisdiction of the government. There were quite a few of these but Radio Caroline was the first and longest-lived - they lasted up to 1990 when the British government gave itself the power to raid radio ships in international waters (!) but it eventually returned with a license and is still around today.

While it wasn't exactly a dystopian floating city (quite the opposite, it was dedicated people who wanted to be there) it's still really interesting from lots of points of view I think.