there is a place with 100 km of here which is privately owned a hunting reserve by a very wealthy family. It has set up for long term survival and is very defensible with small group. Worked out there and saw what I was allowed to… money was not an object they had a concrete batch plant for the amount they poured rough guess 10,000 cubic meters of 35 mpa heavy rebar with elastomeric concrete. There where 24 b train semis driving down that road and came back empty. They had to pass through commercial scale.
So how much room would you need to store 48 semi trailers of gear? And how long would that last you? There are only 3 buildings above ground and zero chance they could hold that amount of goods.
Only reason I know about concrete is they had to get it over the commercial scale. The same with the fuel. 4 trucks 5,000 gallon for that and the pup behind….. that was after build was done. None of the equipment left.
That is some serious prepping beyond what most could afford in many life times.