[Dogpaws]

The fact that the problem is intermittent would raise the possibility of a loose connection, likely the thermostat wire. If the connection is broken, it will likely default to a high or low reading.

Since the dealer has not been able to solve the issue, I would suggest calling Dometic and speaking to a tech. Ask if what you are experiencing is indicative of a thermistor (sensor) not being connected. If this is the case, you could then "wiggle" the connections from the thermistor wire at both ends, the thermistor end and the connection at the rear of the thermostat. If this solves the problem, then you can replace the connector.
It could also be as simple as a staple through the wire.