Could be several issues here ,first check to see if compressor is running ,if not then check why could be as simple as a relay or just a bad compressor. Check to make sure all fan is running that is evaporator that's in the freezer and condenser that's next to compressor.
probably a faulty thermostat as changing settings should make a difference
with fridges ( beverage coolers) the lower the number the colder the setting
have it checked by a technician before making the replace decision
just a thought
if you have the room in the container, consider a water level control unit such as is used to cisterns
they are self contained units that are adjustable for the water level required and fit in a space of around 3" dia and about 12" high
