TomatoUSB

Hi, I'm pretty new to networking, so I'd appreciate any help. I'm using shibby 1.28.0000 MIPSR2-104 K26 USB AIO on an Asus rt-n16.
The Asus is connected as a wireless ethernet bridge to my main modem/router, which handles the internet connection. Wired clients to the asus have internet access, there are no wireless clients on it. What I'm trying to do, is hook up a Nanostation Loco on ethernet port 4, and use it to create a guest wireless network with internet access. I have created a second bridge (br1) and a new vlan (vlan3) on which i have assigned ethernet port 4, and bridge br1. What else do I need to do to give br1 wan access? Thanks