Hi,
Unless you were looking at Gel batteries (which are not, in my opinion a good choice), 500 watts (or 41 amps) is not going to exceed the charging limits of the battery bank.
If you did configure to 24 volts, an inverter could be used to power the OEM converter to provide for all the 12 volt needs. Since the inverter would be needed for the fridge, there is no extra "overhead" penalty for running the converter.
If you did go to 24 volts for the battery bank, you could use inexpensive higher voltage solar panels with a cheaper pwm charge controller. As a bonus the inverter may be a bit more efficient.
