In Webdrive go into File >> Program Settings
in Webdrive:

Select the Proxy-FTP Tab:

As shown above tick "Enable Proxy Server",
leave USER after logon (the default) in the Login Type field, put
the INTERNAL IP address of your proxy server machine in the Proxy
Server Address field, and select Port 10021. (Note: May also
work with port 1080 if you have SOCKS enabled.)
Important: Since you are using a proxy
server, you must tickt the PASV box for Passive Transfers.
Webdrive is now configured to use the proxy
server for connections.