You are right on one count and wrong on the other. I have already said I wish I had made it larger. However, you questioning the use of containers is off-base because it is less expensive and more speedy to build with containers. There is also the environmentally friendly aspect to consider. By my count over 7,000 have responded positively vs 1 (you). I will go with the 7,000+ vs you!
Structural Engineer's Stamp says so. Plus, my companies have written grants many FEMA approved Safe Rooms and built them. I know what materials it takes to pass the Missle Tests that are preformed at Texas Tech to certify per FEMA 361 Standards.