Launchd script to mount volume on boot
The script and the plist work perfectly well if you make following changes:

add a slash in /Users/admin/scripts/monta.sh:

#!/bin/sh
mkdir -p /Volumes/remvol
mount_smbfs //user:password@server/folder /Volumes/remvol


proper ownership of com.jo.monta.plist:

sudo chown root:wheel /Library/LaunchDaemons/com.jo.monta.plist


proper file mode bits of /Users/admin/scripts/monta.sh:

chmod 755 /Users/admin/scripts/monta.sh


load the launch daemon:

sudo launchctl load /Library/LaunchDaemons/com.jo.monta.plist