Breaker Keeps Tripping

If your breaker is tripping when the switch is in either position - supplying power to the water heater or supplying power to the microwave, then the "short" must be between the breaker and the switch. There is no need to look at the water heater or suspect the microwave. The breaker is doing it's job in protecting you from an overheated wire and fire. Take a picture of the switch and label all the wires then take them all loose and see if the breaker still trips. If it does, follow the wire back to the breaker if you can. If not, take the wire off the breaker and find its neutral wire and disconnect it and the ground wire. Then try checking the wires with an ohm meter for a short. When they put your RV together, a screw could have penetrated those wires and shorted them out. If that's the case, you'll need to abandon that section of wire and replace it.

MAKE SURE YOU DO THESE TESTS ON A DEAD CIRCUIT - UNPLUG YOUR RV FIRST!!