I took the easy way out (or so I thought) in rebuilding the Cubietruck (the very low end SSD was showing signs of failure at day #1 but it lasted 2 years before total failure). Instead of Cubian, I installed the Legacy version of Armbian. I burned up most of a day getting the OS installed, the wifi to work without interaction, and getting Docker installed.
The short version (from a couple hour's "research") is that there are two versions of Armbian for the CubieTruck: the Legacy (kernel 3.4.x) version and the Vanilla (kernel 4.6.x) version. The short version is that Docker will not install on the Legacy version of Armbian for the Cubietruck.
The good news is that you can run the following (as root) to upgrade the Legacy (3.4.x) version to the Vanilla (4.6.x) version:
wget -q -O - http://upgrade.armbian.com | bash
Once the upgrade is complete, and the machine rebooted, Docker will install without complaint. Thanks go to "admin" at the Armbian forums, whoever you are...