Well folks, I think I now have the problem "fixed".
As per 3 tons suggestion, I tied in for the shore power supply to the ATS PRIOR to the main panel. This did not completely fix the problem but seemed to reduce the frequency of the GFI trips from about 20% to about 10%.
I then "tuned" the system with an extra 25 feet of cable on the power feed line to the microwave outlet.
After these two changes, I tried the microwave approximately 35 times with no GFI trips. The problem may not be 100% fixed but this is good enough for me.
I don't really understand it but now that I think about it I have had the GFCI on my house trip on several occasions for reasons I don't understand either. Perhaps, as suggested, the removal of the "circular currents" from the main panel connection in addition to the capacitance from the longer cable creating a "smoothing" effect on the system was enough to make the GFI happy.
Thanks very much to those that provided assistance and hung with me throughout this thread. This site is amazing.
Ryan
