Are the tlz packages in the directory you referenced *only* packages I manually downloaded via gslapt? Or, will that directory also include packages that were installed during the original installation from the iso image file?
Those are only packages downloaded when using slapt-get or the graphical Gslapt package manager. Packages installed when you install the system are not copied to the hard drive (unlike some versions of Ubuntu, if I remember correctly).
Something I often do is change the path to the slapt-get package cache. You can do that by editing (with root access) /etc/slapt-get/slapt-getrc. I put the cache onto a removable drive, which means that it can be shared by more than one VL machine, and also gives me a bit of protection against problems on the local hard drive. Only problem with doing this is remembering to plug the removable drive in beofre starting Gslapt or slapt-get.