I think is basically the right idea, but a lot of the details are wrong.
For example, book archivists recommend against storing books in waterproof containers. https://www.sparefoot.com/self-storage/blog/3456-the-sparefo... "Be careful storing books in plastic containers. Because plastic containers form an air tight seal, any moisture residing inside your books will be trapped. If your books are not completely dry before placing them inside a plastic container for book storage, they may develop mold or mildew. If using plastic containers, make sure to insert silica gel packets to absorb moisture."
Instead, archivists recommend acid-free archival boxes. (Gaylord is a recommended brand.)
The other point is that you shouldn't just have one copy printed. Like any important data, you'll want to have backups.
At a minimum, if you have multiple children, giving one copy to each child is sensible; it would make sense for each person to have at least two copies, one to keep at home, and another to keep somewhere else that would hopefully remain safe.
If your document is suitable for public consumption, you could pay for a vanity press to make it available for publication, arranging to have copies stored in libraries. As of today, arranging to have your book archived in the Library of Congress is a reasonable approach to ensuring that some professional archivist will at least try to take care of your book.
(They'll also attempt to digitize your book, and archivists will attempt to care for the digital collection, but, as you noted, there's no way to be sure that any digital equipment will be working 500 years from now.)
But, if your thing is suitable for public consumption, consider another problem: will your great-grandchildren care to read what you wrote? Probably the only way to ensure that anyone will care to read your work is to be/become famous, and to write a successful work with millions of copies. (This also incidentally solves the archival problem: people care about protecting and preserving historically important documents.)
For example, book archivists recommend against storing books in waterproof containers. https://www.sparefoot.com/self-storage/blog/3456-the-sparefo... "Be careful storing books in plastic containers. Because plastic containers form an air tight seal, any moisture residing inside your books will be trapped. If your books are not completely dry before placing them inside a plastic container for book storage, they may develop mold or mildew. If using plastic containers, make sure to insert silica gel packets to absorb moisture."
Instead, archivists recommend acid-free archival boxes. (Gaylord is a recommended brand.)
The other point is that you shouldn't just have one copy printed. Like any important data, you'll want to have backups.
At a minimum, if you have multiple children, giving one copy to each child is sensible; it would make sense for each person to have at least two copies, one to keep at home, and another to keep somewhere else that would hopefully remain safe.
If your document is suitable for public consumption, you could pay for a vanity press to make it available for publication, arranging to have copies stored in libraries. As of today, arranging to have your book archived in the Library of Congress is a reasonable approach to ensuring that some professional archivist will at least try to take care of your book.
(They'll also attempt to digitize your book, and archivists will attempt to care for the digital collection, but, as you noted, there's no way to be sure that any digital equipment will be working 500 years from now.)
But, if your thing is suitable for public consumption, consider another problem: will your great-grandchildren care to read what you wrote? Probably the only way to ensure that anyone will care to read your work is to be/become famous, and to write a successful work with millions of copies. (This also incidentally solves the archival problem: people care about protecting and preserving historically important documents.)