Dehumidifiers exhaust hot air inside. It will keep the RV dry, but very hot. You will also have to empty a tank or drain into a sink and then empty a holding tank now and then. They are good for cool, damp climates.
We have 30amp hookup beside the house. We run the AC. It is set at 90. That way we can use the RV as a extra room or retreat or guest house. The cost to run either dehumidifier or AC seems to be close. No real advantage to putting up with the heat and draining.