While I'm not finished, I've now got a working version of the driver that will open and/or close the shutters sequentially (one side first, then the other), and which presents the correct status when polled [...]
Bravo!!! Nice work, and I am sure quite satisfying!

I'm grateful for the wonderful help from the ASCOM team of Tim Long, Peter Simpson and, particularly, Rick Burke. They have patiently helped and encouraged me through the steepest parts of the learning curve, and helped solve a few issues that stymied me along the way.
Those people really deserve an award for helping change the face of astronomy by enabling software control of astronomical devices. Especially Peter Simpson who has tirelessly and consistently worked to provide the ASCOM Platform and a bunch of helper tools for app and driver developers.