Foolish at best.
When the SHTF, the site has its vulnerabilities: fresh air intakes are needed for all systems, especially the generators that produce tons of heat. That heat has to be exhausted - clog the exhaust point, obstructing airflow and systems overheat and fail.
A bad guy can poison the air or cut off airflow and everyone below is toast. Assuming the intake vents are hidden - they can be found......
The vanity of man thinking he can make himself invulnerable with his money.
Like the proverb, “A pawn and a king both return to the same box after a chess game.....” We all came from dust, and will return to dust, taking nothing with us other than what was done for eternity.....
“The vanity of man thinking he can make himself invulnerable with his money.”
I’d rather be hunkered down in the middle of a forest. With the option to be mobile and relocate if necessary.