This is NOT your typical Garry's Mod addon.
All kinds of nodes and polished navmeshes for Garry's Mod maps, made for KM_CM's Addon. Saved in folders in format "[MapName] [Version]". Note that if versions are different, it might not work.
You can check your map's name and version by running lua_run print( game.GetMap() .. " " .. game.GetMapVersion() ) in the console as a superadmin.
Example output: gm_construct 1765
To install, you have to manually put nav files in /garrysmod/maps,
and json files in /garrysmod/data/covers/ (create covers folder if it doesn't exist).
Don't forget to backup the original nav files, or some consequences might happen, such as you being unable to play in multiplayer... without the other installing the new naw too... I think... I have no idea to be honest xD
If you really feel like installing the cover nodes onto a different version of the map,
just change the last digits to the output of game.GetMapVersion(). But note that they may break.