I want to share my experience with my external ext 4 drive.
Every time when i rebooted my raspberry the file access rightd where wrong. root:root instead of pi:pi
Before the mount the mount point had the propper right in /media/usbdrive
and a default entry in /etc/fstab
But when i finnaly changed the mount point to /mnt/usbdrive and changed fstab, the propper owner (pi) stayed the owner after mounting.
Now i can remote write on the drive when i connect with afp as user pi