Seen it before. Your board and heating element in the fridge are most likely gonners. $250
You converter, which is escentially a battery charger, is also gone. Depending on brand the internal fuses or resistors might have saved the transformer, but the unit is not fit for commercial applications anymore because if there is any problems in the future and you repaired the converter, their lawyers are coming after you.
Buy a new converter, $200 or so.
Test you GFCI, they should be fine.
Renter needs to pay. It was his negligence. Call him and tell him the total of the damage and let him handle the insurance.
RV share has to help, is part of their responsibility to broker between you and the customer.
I have dealt with similar problems in the 7 years we have been renting out fleet. RVSHARE is NOT free and clear. Don't let them off the hook. They can charge the customer as they have their credit card