We are on the same path it seems, here is the install that finally worked for me after many hours.
put the lan cable in the LEFT port (lan1)
use nano or vim to edit /etc/network/interfaces
iface eth0 inet manual
iface lo inet loopback
iface lan1 inet static
dns-nameservers 192.168.1.124 18.104.22.168
pre-up /sbin/ifconfig lan1 up
Like the poster above said the pre-up takes care of getting eth0 up first, the rest is knowing lan1 is the left port! Love the documentation huh?
Edit; I haven’t tried but I assume if you substitute lan1 for wan in the above you can put the cable in the RIGHT lan port and it should work.