We rented a class A a few years ago. My rule was strictly to remain seated and belted at all times. Even to the point that I pulled a full-on 80s-dad move and literally pulled the RV over to physically enforce the seated/buckled. After two of those, the children decided that no amount of seatbelt discomfort was worth the headache, and the wife had had enough of the lost time, so everyone stayed buckled after that.
It seems that most of the listings indicate the number of seats/seatbelts so make sure to match that to your number of occupants and you should be good.
FWIW, some have indicated to me that transit/sprinter style are safer in an impact than class c. Not sure re: class A. And obviously nobody should be riding in a 5th wheel or other trailer typle while moving.