This document will help you with installing Tunneling and testing it.
What is tunneling, I explain it as a VPN (tunnel) to QVS. The plugin talks to the Qlikview server on port 4747. If this port is blocked then the plugin will give an error. So if IT will not open port 4747 and you have customer that want to use the plugin you can setup tunneling. With tunneling enable the 4747 traffic is repackage an sent as port 80 traffic.