after the disc check in pre-boot I have now 2 mkdirs to create both ftp dirs
then I have in fstab the mountpoints and it works

Filesystem 1k-blocks Used Available Use% Mounted on
/dev/root 3072 3072 0 100% /
/dev/discs/disc0/part2 3850320 541052 3113680 15% /opt
/dev/discs/disc0/part3 476331024 118551016 333583712 26% /mnt
/dev/discs/disc0/part2 3850320 541052 3113680 15% /tmp/mnt/disc0_2
/dev/discs/disc0/part3 476331024 118551016 333583712 26% /tmp/mnt/disc0_3
a bit stupid that I couldn''t figure the mkidir myself out
well, it totally works now
I do think it scans the drives double now, but hey, then you''re sure no errors are left