Hello Martin78
I'm not an advance unix guy, nevertheless, I did setup SCP/SFTP after adding the fun_plug. It is not hard, however, I cannot remember exactly how I did it. Nevertheless, you just have to make sure you define the user, its home dir and the rights permissions.
Google for command "chmod" or just follow some of the same commands you did for fun_plug root user such as creating its home dir and file permissions. That is what I did at least for 0.5 version.