After some 5 weeks of testing and just living with the periodic timeout errors, I *think* I have solved it. Always tricky to declare an intermittent problem solved when it often does not occur until 6+ hours into an imaging session, but I am cautiously optimistic.
The problem? This 12v splitter:
It came with the ZWO add-on dew heater that I bought because the internal window heater in the RisingCam was not sufficient on particularly humid nights. I have run at least 20 hours of testing with a different 12v splitter with no crashes or timeouts.