Not too much of this setup makes sense. Most 1985 RVs other than large Class A rigs would have been 30 amp rigs. I wonder if one of the previous owners thought they were tripping the breaker too often so they replaced the 30 AMP breaker with a single pole 40 AMP as a band aid cure. Personally, if I wasn't comfortable with the electrical circuits I would have an electrician check it out. They would be able to determine whether or not the panel is a 50 amp panel. They would be able to trace the wiring to the point where a shore cord would need to be attached and they would then be able to check all the connections and wiring to be sure any modifications were correctly done. It would be a few of hours of hired help that might prevent a serious accident.