UPnP and NAT-PMP when using policy based routing?

[TheLinuxGuy]

I have "UPnP and NAT-PMP" working just fine on my regular WAN when traffic is from LAN.

I have a new interface for my VPN_WAN which I am successfully using as the gateway for some hosts on my network. I am wondering how to make sure that UPNP can work as it does on my LAN but with this new gateway?

Are there any special settings? I am not sure about adding my VPN_WAN to my "External interfaces" which already contains "WAN" - what is the right path?