Bummer, you will need to go over all systems to be sure all are ok after a unit has been sitting this long. The problem with the water heater is the fact that there is debris, be it spider webs, mud dobbers, lizrds carcuss, any thing that is not supposed to be in the venturi, (tube from gas valve to burner) and also in the burner box or tube in this case. All this needs to be cleaned out.
The refrigerator, as stated, probably has a short. I would recommend removing the outside vent access cover and visually inspect for the presents of mice or squirel nests. THey can chew up the wiring harness and cause big problems. You will also want to check the furnace for the same debris as the water heater. The air conditioner could have nest in it too. The holding tank valves could leak and the toilet may not hold water in bowl. It may take some effort but it can be brought back around if the damage by rodents is not too bad. Good luck and let us know how you do.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7