A method of forming a bendable slotted liner with multiple circumferentially overlapping non-axial keystone slots comprising: transversely profiling a rod to form a profiled rod, having bending members outwardly profiled wider than intermediate and inward widths, interspersed with bases profiled to bondably mate with axially adjacent bases on a neighboring winding; forming the profiled rod into alternating port and starboard bending members and base pairs, by one of, bonding transverse spacers to the rod, transversely corrugating the rod, and forming the rod with one of transverse outdents and indents; winding the profiled rod to the outer diameter; and bonding axially paired bases together; wherein configuring the non-axial slot circumferential length greater than the circumferential base length on adjacent rod windings, forming non-axial keystone slots between bending members providing axial strain relief, with outer slot widths within a prescribed slot range and axial strain relief capacity greater than 0.1%.