temperatures

Well, the fridge is usually a problem with air circulation to the coils and or outside air temp being HOT. It can only cool so many degrees down from the outside air temp. An RV refer is like putting a refer outside with the coils outside. Putting an aftermarket fan in the coil area to exhaust the heat out, can help, but still, it can only do so much on a hot day with the sun blaring down on that side of the trailer.
The water heater problem can be one of a couple of problems. First of all, is it on gas that it is too cool, or on electric. Either way it is most likely the thermostat of that system that is at fault. The gas and electric systems are completely different systems with their own thermostats.