(This was originally filed as SeattleTestbed/dist#133).
The custominstallerbuilder installer packager script takes a base installer for an OS and adds the vesselinfo file to it (which contains the share sizes and user keys for the customized Seattle VMs). For the Linux installer, it does so by gunzipping the base installer, piping it through tar, appending file ./seattle/seattle_repy/vesselinfo to the tar file, then regzipping it. Note that all of the other contents are in a slightly different dir, with identical expansion on an interactive terminal, but still distinguishable in the tarball:
seattle/seattle_repy/deserialize.repy
seattle/seattle_repy/math.repy
seattle/seattle_repy/servicelookup.repy
# etc., etc.
./seattle/seattle_repy/
./seattle/seattle_repy/vesselinfo
When the person installing Seattle on their machine from the completed, downloaded installer tarball uses a GUI tool like Gnome's File Roller to extract the contents, they might only choose the "seattle" directory, but miss the "." dir that is shown separately. Too bad, "." contains the vesselinfo!

If you happen to extract the tarball on the command line instead, tar+shell result in "seattle" and "./seattle" expanding to the same directory, and the vesselinfo file will be placed where it should be.
The fix will be to make packager.py use the correct dir (without the leading ./).