I once read about a family who lived in a house for two years without knowing there was a basement. The previous owner had a water problem and cemented off the basement stairs and outside well windows. I thought that if these people could not discover the basement in 2 years what chance would marauders have of discovering it in 15 minutes.
As a builder I design and sell homes that are poured concrete in insulated foam (ICF). With secret access, a well in the basement, combination air and secondary exit. We use buried propane tanks for cooking fuel and a buried oil tank for heating. Wood stove later. There is no evidence anywhere that the basement exists. The upstairs is also 8” concrete and 100% fireproof floors, furniture, metal cabinets, etc. We use completely separate systems for the basement and the house above.
Anyone approaching the house sees some broken windows (stored in basement) and debri. A desolate house and a bottle of skunk scent on a toy stuffed animal in the corner of the pantry will make invaders stay very short.
Until law and order of some type returns, the occupants live very comfortably and only come out at night if they wish. Crops and evidence of occupancy won’t appear until law and order does. Most have a three to five year food supply for them and relatives. The homes are planned in a central location of relatives who will be invited and not more than 50 miles away from the primary occupants residence to allow for having to walk or ride a bike.
There are far more “Undiscoverable” retreats around than you know. All of my trades people are from way out of town and the buyers are thoroughly schooled on secrecy. One viewing the the Twilight Zone “The Shelter” is all it takes.
Good luck.
WAY Cool! So many things out of my price range...
DIY kit?
YOur plan sounds nice but out of my reach. I am more concerned with the heat, and other detecting eyes of the feds. You cannot hide from them