As you mentioned you could leave the A/C running but if it should shut down it could getting brutally hot inside. It might be a better option to leave the A/C off and keep windows partially open in the RV. You would probably want to break up your day at the park to return to the campground to check on them at some point during the day. The bus transportation from Ft. Wilderness to the parks runs on a regular basis and has pick-up/drop-off areas near each section of the campground.
Beyond that, have a great time :). My wife and I camped there back in April and had a wonderful time.