Here's why:
1) It's Florida, you can run all the dehumidifiers in the world and it won't dry out the whole state.
2) Dehumidifiers put out a LOT of heat. So while the air may dry up a few percentage points in your RV, say from 86% to 80%, the temperature in RV will shoot up to an uncomfortable level.
3) Better suggestion - run the A/C in the RV. A/C's are supposed to remove moisture from the air, as well as chill the air. Make sure your A/C coils are clean and if everything is working well and you don't have a refrigerant level problem, you'll be fine with the A/C. Let the thermostat control the temperature in the RV even when you're not in it. There should be nearly a steady stream of water dripping from the A/C when it is running in a climate like Florida, maybe not so much in AZ.
4) Wear loose fitting clothes made of cotton. Technical fabrics like runners wear work great here in the South for making you feel cooler.
5) Bring some Zyrtec or other OTC allergy medicine, because we have pollens and other things that will send your desert dwelling sinuses into a frenzy.
6) Use a small fan or fans to move the air around inside the RV, that will help if feel better too.