I'm using tomato firmware 1.28 by shinny and I need to create a vlan for Port 3 as external router in Pisowifi Vendo.

I want to use tomato router as my main internet provider with a dual wan enabled wherein WAN, Lan1(WAN2),LAN2,LAN3,LAN4 are the default port settings....the wan1 and wan2 are connected to 2 different ISP or modem. But I want to create a separate VLAN for my Pisowifi wherein the LAN4 is going through Ethernet port of raspberry pi and LAN3 will be going to my external AP of my PISOWIFI.
The Pisowifi has an IP address of 10.0.0.1 and it gets it's internet access from tomato through...

I'm using tomato firmware 1.28 by shinny and I need to create a vlan for Port 3 as external router in Pisowifi Vendo.