Thanks for the help everyone! With all the suggestions and troubleshooting hints, we were able to trace down the location of the coach power relay and bypass it! On our 99 Contessa Naples it is located on the inside of the firewall at the foot of the bed. The are three large solenoid relays there, and by using a voltmeter across the coil terminals (the two small control terminals with 16awg wire) we were able to determine which of the three relays it was by measuring the coil voltage momentarily appear when the switch was toggled. Having determined which relay it was, it was then just a simple task of bypassing the relay by transferring one of the big 02awg cables from one terminal to the other so that both big cables were bolted to the same terminal. Coach power is now rock solid!
P.S. The defective solenoid had poor contacts internally and was heating up due to contact resistance and dropping 1.5V across the contacts with less than 20A being drawn by the coach house systems (inverter, water pump, interior lights, etc.)!!! It should normally have dropped less than 0.02V if the contacts were good.