I mounted it with the Cloudron build in mount option in the UI. Are there other options? I guess editing fstab by hand will be overwritten at some point 
Here is the output of the mountcommand from the console.
root@81deeb68-0628-45ff-bf4c-0e9e294e7935:/media/FSN1-BX1401# mount | grep FSN1-BX1401
//u452885.your-storagebox.de/backup on /media/FSN1-BX1401 type cifs (rw,relatime,vers=3.1.1,cache=strict,username=u452885,uid=808,forceuid,gid=808,forcegid,addr=2a01:04f8:2b03:0981:0000:0000:0000:0002,file_mode=0666,dir_mode=0777,iocharset=utf8,seal,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1)