The reason these folks are crowded into camps has nothing to do with available space/area/square measurements to put them. It has everything to do with infrastructure and social structures to absorb them.
There are Palestinian refugee camps in surrounding Muslim/Arab nations where 4th and 5th generation “refugees” are still kept cloistered living in squalor, not allowed to find work or become citizens in the country where they were born. They are kept there to maintain the “crisis”, because the no one wants to solve their problems. They want to use them as leverage.
Even in crowded Europe, the problem with absorbing refugees is not the space to put them. The infrastructure to absorb additional tens of thousands instantly is not really there, but the far bigger problem than numbers of people is integrating them into a place that doesn’t use their native language, where social expectations are greatly different, where job skills and life skills don’t match up to their experience, and where people don’t really want them.
Seasteading has zero infrastructure at the moment. None of the above problems are currently solved by seasteading, and the cost of building that infrastructure keeps being estimated so high by TSI, that it is extremely unlikely that TSI will develop anything but a curiosity or escape hatch for the extremely rich.