In the last episode (Mar 15), Mikhail Teterin said:
You might have a device that's not known in umass's table. It looks
like it needs to know the protocol before it will create a da* device;
try editing /sys/dev/usb/usbdevs and adding a DISKONKEY3 entry (usbdevs
-dv should print the hex IDs you need), and copy one of the existing
DISKONKEY array entries in umass.c.