Cats are creatures of habit, does she ride in the car with you?
Or has she just been a stay at home kitty? My advice is to take her along she may eventually get used to riding in the RV. Until then if she hasn't rode with you in the car, try that maybe the motion of the vehicle is freaking her out.
When we moved to our new house, Kola lived in the master bedroom closet for over a week. She was terrified of the ceiling fan and we didn't let her outside for 2 weeks. We have been here over a yer now and she has just gotten used to going outdoors again for hours at a time.