It is disclosed a densely packable sequential series of external housing units associated with succeeding internal housing units. The external housing units have inside volume and openings for receiving the internal housing unit. Means for facilitating the displacement of an internal unit out of an external unit, like integrated bearings, integrated wheels, integrated retractable wheels, and a low friction coating are installed on an inside shells of the associated external housing unit, on an outside shells of the internal housing unit. The housing units have a uniform cross section along a majority of one of the dimensions of the unit, having outlines like a circle, a triangular frame, a rectangular frame, a circular arc of, a trapezoidal frame, a polygon of five, six or more edges, a hyperbolic arc, and a parabolic arc, or other types of arches. The typical transverse linear size of an internal unit is 80% to 99% of the preceding external unit. The series is transportable as a single cargo item between locations. A shell of an housing unit may include at least one layer like highly insulating layer, anti-ballistic layer, and composite materials such as fiberglass reinforced plastic layer, polymer-metal composite layer, and carbon based composite materials.