Apparatus and methods that can be used to stabilize a portion of an extended-reach tool assembly to enable the dimensional mapping, non-destructive inspection and/or simple repair of elongated and serpentine structures used in aerospace and military platforms. In some embodiments, a jointed (i.e., articulated) arm of the extended-reach tool assembly, which is mounted and manipulated at the entrance to a limited-access space (e.g., a cavity), is equipped with actuatable contact pads or bladders to stabilize the distal end of the arm to which a tool-carrying end effector is coupled. The end effector is capable of holding and orienting a probe or sensor (e.g., NDI sensor unit, laser scanner, camera, etc.) or other tool (e.g., drill, sander, vacuum, “grabber”, coating sprayer, etc.).