Thanks for the links. I really want flatpak to work for me because I like the sandboxing but the storage thing is a bit of a killer for me at the moment and I could not for the life of me get Digikam, Shotwell or Rawtherapee to hand image files over to GIMP with the flatpak versions, whereas the repo versions were fine out of the box. Also, I feel like flatpak programs are much slower to open but that might just be me.