I thought you were going to mention concrete canvas, which stiffens into a semipermanent (10 year) structure when wet: https://www.concretecanvas.com/us/cc-she

I thought you were going to mention concrete canvas, which stiffens into a semipermanent (10 year) structure when wet: https://www.concretecanvas.com/us/cc-shelters/ https://www.concretecanvas.com/us/cc-shelters/ Bring your own cave?