This is what I have in my /etc/udev/rules.d/90-locobuffer.rules file:
SUBSYSTEM=="tty", ATTRS{product}=="LocoBuffer-USB", ATTRS{serial}=="FTNO3P86", SYMLINK+="ttyUSBLB"
SUBSYSTEM=="tty", ATTRS{product}=="USB-Serial Controller D", SYMLINK+=“ttyUSBLBII"
and in 91-dccex.rules:
SUBSYSTEM=="tty", ATTRS{serial}=="75435353934351F0B121", SYMLINK+=“ttyUSBDCCEX"
and these do the trick for my three USB command station interfaces from my pi.
Your serial number is probably different.
david zuhn