First of all, they have to be close to a somewhere they can buy more supplies - food, toiletries, diesel/gas, etc. They can't just build in the middle of the sea, they've got to be near somewhere where they can easily land a small boat within easy reach of a supermarket.
That doesn't really look that they're really "independent from the State". Even if they only went on shore to buy necessary goods and paid necessary services like medical emergency treatment with their own money, they are using a State's infrastructure, like roads, ports etc.
I'm sorry, I think seasteading doesn't have a future if it's not carried out with LOTs of planning, and preferably by a major group of people. Anarchy isn't only about "not paying taxes". It has also to do also with finding alternatives for the services states provide to you.
I hope the best for him, but his plan simply doesn't look sustainable.