Pulling my hair out trying to figure out how to set the URI for Zenoss to work behind an Apache mod_proxy setup, I figured out the solution is to use a rewrite rule on the virtual host within Apache. Here’s the rule I’m using:

RewriteEngine on
RewriteRule ^/(.*) http://internalserver:8080/VirtualHostBase/http/externalserver:80/VirtualHostRoot/$1 [L,P]

Of course, change “internalserver” and “externalserver” for your hosts, and “externalserver” should match your ServerName definition in the virtual host config.