The joys of an old Citroen. Well if you make sure that there are holes in the door bottom for the water to drain out of and coat all the inside with rustproofing wax like Bilt Hamber Dynax then it should outlast your ownership….
I have seen the occasional Traction with rubber strips from a modern car retro fitted but as far as I am aware Citroen didn’t fit anything. Slough cars are worse than French BTW as when they cut holes in the B pillars and fitted the trafficators they didn’t put drain holes in the sills so…..
Oh and make sure you put a polythene barrier between the door frame and inner door car to stop them getting damp, warping, staining and rotting
Good luck