I don’t think a mounted veichle item just for repairing guns is worth installing.
Guns rarely break or get damaged and the fire arm repair kit / gunsmith repair kit consume so little that installing a mounted version is completely obsolete.
Gun mods only require a screwdriver, nothing else. So unless someone overhaul the guns system, this is pointless.
Now a veichle sewing machine would be more useful as the player can repair/reinforce and modify clothings. The only problem is the thread, tough.