The strain gage wire must have some resistance but it'll take a lot of low resistance wire to get all the terminals in one location.
No one wonders "where am I going to get 3" of wire with a low enough resistance" to wire up common thumb nail size strain gages.
Prestress isn't a problem with strain gages. Just stay in the elastic region. Moreover, in this application 4 sig figs might not be necessary.
Also decreasing the sag/length ratio of a catenary increases the sensitivity. A small displacement in the horizontal causes a large increase in tension and resistance.
They already get down to a few microns in the millihertz range with motion detectors. The goal here is longer warning times meaning small displacements at even lower frequencies or DC velocity. Higher frequency noise can be filtered.
If necessary the wires could be under or inside PVC.
The resolution needs to be one part per 100 billion.