Mark explained it more succinctly than I could
I did not touch the factory-installed thermostat; didn't want to spend that kind of time trying to modify/use the original thermostat. Mark is exactly correct about the purpose of the added thermostat.
With the model of RS2000 I used (apparently the only one available last summer) it really was a fairly simple swap-out of the Dimensions for the Xantrex. There were two somewhat complicating factors with the swap:
a) Dimensions doesn't use terminal lugs on the 12V source input - they use a screw capture of the wire ends
b) Running the new Cat5 cable from the inverter to the new control panel was time consuming. The existing eight conductor cable from the Dimensions to the remote display is NOT compatable with the Xantrex interface
The existing Winnie battery voltage monitor in the OnePlace is still there and I use it occasionally to look at battery voltage. However, now with my Xantrex system (with auto gen start - AGS) and the Echo~Charge, I never have to worry about the state of charge under usual camping conditions.
If we boondocked, I would need to be more aware of the battery condition because we have quiet hours programmed into the AGS; the genny won't start between the hours of 9 PM and 8 AM, so it would be possible to drain the house batteries overnight. (However, if we did boondock by ourselves or at a truck stop, I might remove the quiet hours.)