If it is direct from the battery in the camper it would be live all the time. If you run the charge wire from your navs battery to the camper and it goes through a battery charger of some sort then the power will normally only go one way due to the charger. Most cars that tow vans have what is called a hot wire that charges the battery and runs the fridge while driving. But due to most caravans having a cteck or some other type of charger in them once you disconnect the trailer plug the power will only be present on the car side of the plug and not the caravan due to diodes in the cteck not allowing it to travel backwards. Hope that makes sense and answers your question.
Cheers