@doniks I finally got it working! I had to use the -w flag when doing the fastboot commands.

The full steps I used for the successful flash:

ubuntu-device-flash touch --channel=ubuntu-touch/stable/ubuntu --device=flo --bootstrap
# Reboot into bootloader
fastboot flash -w boot boot.img
fastboot flash -w recovery recovery.img
# Boot into recovery
ubuntu-device-flash --server http://system-image.ubports.com touch --channel ubuntu-touch/rc-proposed

@doniks Definitely:

mark@coachz:~/Downloads/deb_images$ ubuntu-device-flash ubuntu-device-flash --server
http://system-image.ubports.com touch --channel ubuntu-touch/rc-proposed --bootstrap
2016/09/10 13:33:52 Expecting the device to be in the bootloader... waiting
2016/09/10 13:33:52 Device is |deb|

@doniks Yes, I followed the instructions just as shown; ran the --bootstrap command, flashed the boot.img and recovery.img, booted into recovery and ran the second flash command.

I attempted to follow these instructions, but after I see the message "Rebooting into recovery to flash" in the terminal, the tablet gets stuck on the "This phone needs restoring from a PC..." screen.