I would think that a medium to heavy weight steel-truss frame or heavy timber platform attached (maybe series of wide rubber belts looping around) on each fender for support would seem like it could work, or not. Then you could build pretty much "anything" you want on top.
I could imagine building a homestead on this; with topsoil, garden, chickens, solar/wind power and solar distiller and low-profile masts.
The logistics of being "sovereign" might be an issue though, unless you live in the high seas all the time.
If only I don't get sea-sick.
"society could go in a thousand directions as to how it would exist and how it would be, but the public mustn't know that. The generations must believe that the one that they're born into is naturally evolved."-Lenin/Alan Watt/cuttingthroughthematrix.com
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