Update:  Discovered that the bed doesn't stay within the required temperature if ambient is low or there's even a slight breeze.   I'm going to upgrade the bed heater to use 24V. This involves adding a 24V PSU,  a MOSFET, and rerouting some of the associated wiring.  Also, on the advice of my 3D printer hacker friend Jason, I am upgrading to heavier bed springs and Z axis bearings.  

So that's the plan, but don't have a schedule yet, sorry. Like everybody, I have too many other things going on that compete for time. Follow if you're interested!