CST's underground vaults...
"A description of the property just south of Eureka - a little place called Petrolia - gives some details of one of the vault sites. The 3000 acre property includes buildings assessed at $2,024,570. The scriptures are intended to be kept in an atomic-bomb proof vault 374 feet below the ground. This vault is assessed at $8,429,259. Here, the paper on which Hubbard originally wrote is treated to ensure that it lasts for at least one thousand years, and his tapes and lectures are transcribed onto gold-plated CDs." - Jeff Jacobsen
See the CNN report
More info on CST underground constructions: http://www.holysmoke.org/cos/petrolias-new-neighbors.htm
But why investing in a bunker? Security of upper levels is hardly any real concern as anybody can go on the net and find it. It could be hide away in safety boxes around the globe. The question remains...