But in Linux, it is almost always that there are a number of ways to do things for your PC and this is my way of updating an internet-less Ubuntu box.
On an updated PC where I configured it not to delete the downloaded (and updated) deb packages located at /var/cache/apt/archives, I copy the contents of that folder to a folder on my home directory, thus:
$ sudo cp /var/cache/apt/archives/* ~/Desktop/updeb
I then burned the contents of ~/Desktop/updeb folder to a CD(s) with GnomeBaker or any CD Burning app of your preference.
Now going to the internet-less PC, copy the contents of the CD containing the updated deb packages to a folder at the home directory of the internet-less PC.
$ sudo mkdir ~/deb
$ sudo cp /media/cdrom/* ~/deb
Now go to the directory where you copied the packages
$ cd ~/deb
Do this while in the said directory to create Packages.gz:
$ sudo dpkg-scanpackages . /dev/null | gzip -9c > Packages.gz
Open and edit /etc/apt/sources.list to add the local folder as a repo…
$ sudo gedit /etc/apt/sources.list
Insert the following line at the end of the file…
deb file:/home/username/deb/. /
Save and close the file. Update and upgrade with Synaptic or at CLI!
$ sudo apt-get update
$ sudo apt-get upgrade
P.S.: Make sure you have installed the dpkg-dev package on the internet-less PC from the Ubuntu CD Installer before anything else.
$ sudo apt-get install dpkg-dev
I hope this helps!