that should work. You need to run that in the same shell you run the rclone mount in. Also you’ll probably want a leading / so export XDG_CACHE_HOME=/mnt/user/tmp
That is a different issue. The Union mount needs to implement the optional Methods Move, Copy, DirMove etc. It might be better to embed the fs for this…
Can you please make a new issue on github about this - it should be straight forward to fix.