Kind of depends on the maker of your heater. If an Atwood, then no anode rod is necessary.
If a Suburban, then I would use use one because eventually the inside will corrode due to the water being present, even if only part time. The one that comes with the Suburban should last quite a long time though. Just inspect it when you pull it out to drain the heater. When it gets to looking like a rough piece of thin pencil then replace it.
Barney