Thanks to this thread I've got mine working
I'm using an old Maplin kit on a brand new Pi 3+ and my COM port is /dev/hidraw0 though - found this through dmesg:
[ 129.360674] usb 1-1.2: new low-speed USB device number 5 using dwc_otg
[ 129.526448] usb 1-1.2: New USB device found, idVendor=1941, idProduct=8021
[ 129.526463] usb 1-1.2: New USB device strings: Mfr=0, Product=0, SerialNumber=0
[ 129.559936] hid-generic 0003:1941:8021.0001: hiddev96,hidraw0
: USB HID v1.00 Device [HID 1941:8021] on usb-3f980000.usb-1.2/input0
Interesting description on lsusb:
pi@CumulusMX:~/CumulusMX $ lsusb
Bus 001 Device 005: ID 1941:8021 Dream Link WH1080 Weather Station / USB Missile Launcher
Bus 001 Device 004: ID 0424:7800 Standard Microsystems Corp.
Bus 001 Device 003: ID 0424:2514 Standard Microsystems Corp. USB 2.0 Hub
Bus 001 Device 002: ID 0424:2514 Standard Microsystems Corp. USB 2.0 Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Not quite got the web upload working right though yet (trends and graphs aren't working and it never created the graphconfig.json file - I had to do that myself).
EDIT - forgot to update this last night - I just copied over the 'webfiles' directory structure to the web server and it's fine now.