On a new construction home, I can do one for ~$4,000.00 my cost.
Retrofit is ~$10K in the existing slab, or ~$6K looking like a shed.
Two of these survived the May 1999 EF5 (the tornado the caused the "F" to become the "EF" scale).
Any other questions?
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I do the things that I must, and really regret, are unfortunately necessary.
RIP OBG