Software :: Update Base System And Customize ISO

A year ago, I customized an Ubuntu 7.10 iso following this guide: [URL]. However, I want to update the base system of my customized iso to at least Ubuntu 8.04. How do I do that? One idea I think may work is:

Code:
sudo chroot ./isonew/custom
mount -t proc none /proc/
mount -t sysfs none /sys/
export HOME=/root
apt-get update
apt-get upgrade
apt-get dist-upgrade
apt-get clean
rm -rf /tmp/*
umount /proc/
umount /sys/
exit

But, I am not sure if it works (I tested it once, but then the power went off when I was 80% done with the download which took 2 hours on my slow connection. So, I don't want to waste 2.5 hours to see that it failed)?