The number doesn't need to be that high. 30000 sealed actions doesn;t mean 30k indictments. An action can be anything from a filing to a wiretap.
One indictment can also cover many individuals. I'm making my count based upon known available space. We have(with the expansion) about 15000 beds at gitmo and an unspecified number at a secondary location.
Best guesses for that are floating prisons in the Pacific and Diego Garcia.