I haven't tried Plone the way you're trying (I've used an Apache rewrite rule), but it may be something to do with port 8080, which I think Squid uses, so Apache may be stopping you - not sure though. Did you stop and restart Plone after you'd made the change?
Are you using the RPMs I posted here? I've configured Plone to use 9080 instead. If you'd like information on the rewrite rule, let me know.
Des