Sharing Airport Extreme with attached HD over WAN to Windows

So I've never gotten this to work. I have three external HD's attached to my airport extreme, the extreme is set to share over WAN, and any Mac can connect with zero problem using AFP. However, I've never had a Windows computer connect successfully using Samba. I have connected over LAN on windows just fine (not with Samba, of course, just with the built in windows systems) but I've never had anyone using Samba be able to connect from over the web.

Has anyone else had this work? Any guidance to offer? A friend of mine said the Samba port (445) was closed on my IP - because this is being shared via the Extreme, I can't very well set port forwarding to deal with this issue, so I'm clueless. Help!