A possible seastead business model I haven’t seen proposed to date, is long term vessel storage.
The seastead would have the (protected) location, the experience and manpower for marine vessel operations and security operations, presumably some equipment for on-going minor (and possibly major, with a semi-submerisble dry dock) vessel maintenance and repair.
It could probably be written into some contracts for “on-site” security to have a watch standing crew residing on the vessel during mothball to exercise systems and maintain things. There’s a cost (in maintenance and fuel) to have a ship sitting idle. @Ellmer might have more details, but I imagine refrigeration systems, hydraulic seals, and engine gaskets (including seals and gaskets that are designed to be regularly immersed in lubricant to keep them from drying out and cracking) all benefit from being kept in a low activity but regularly exercised status to avoid deterioration. Batteries don’t stay charged forever. Bird feces don’t clean themselves off. Freshwater systems build up biologicals if not flushed regularly. Leaks and corrosion don’t monitor themselves.