Foundations and the people working in them have limits and liabilities.
Depending on the nation they are registered in, they are bound by the laws of that nation (laws which often collide with the full human rights).
Secondly, lobbyists aiming to misuse such a foundation can easily cripple a state-bound organization through local politicians. In any case a state-bound organization risks loosing its coherence during societal collapse of the state(s) it is registered in.
Last but not least, a non-state cannot take on the responsibility of refugees and stateless, to grant a nationality, citizenship, passports, etc. Therefore a true nation state established in cooperation with United Nations is the strongest starting point for Forever Fleet. There is nothing new to this concept with city states having been common for centuries - several well-known such as Luxembourg and Monaco - with many more unrecognized micro-nations having sprung up since the 1960s. The reason for these micro-nations not being recognized, is generally that they have claimed territory inside the interest zones of other states - whereas Forever Fleet only claims territory on its own ships and usually more than 200 miles off the coast of any sovereign state.