[Grml] grml-halt on usb disk, for writing on unionfs

[pat]

hi there

i have installed grml successfully on my cf card. i'm searching a way 
how to write my new configurations and files on the disk. i've found a 
way how to sync an unionfs with the originaly readonly mounted 
directory... but i'm a bit confused. i don't now how it should look like 
in the grml debian derivate.

here is the original debian wrap script:

#!/bin/bash   
# halt-wrap
mount -o remount rw /OLD_ROOT/real_root
rsync --delete -abRvz --exclude "/sys" --exclude "/proc" --exclude 
"/dev" --exclude "/OLD_ROOT" / /OLD_ROOT/real_root/
halt

should i copy this script in /usr/sbin or put it in /etc/init.d/ and 
modifier the /etc/rc.conf ( or something i don't remember anymore... 
because i'm using the symlinking stuff )??