It seems that my Gotham installation is not detecting the skins that I manually copy-pasted to the userdata/addons folder. I cannot find the cause, all seemed okay. And yes, the skins I am trying to install are Gotham compatible.
userdata/addons isn't the correct location.
place them in ../xbmc/addons instead of ../xbmc/userdata/addons.
likely he places them in the correct place (make sure you place them alongside other addons in userdata) and don't forget to actually restart xbmc/kodi.
No restart=no showing of the addon
Thanks for your replies. I have placed the skins alongside other addons, and I also have restarted xbmc/kodi. Should I produce a debug log?