We have a fantastic fan in our bedroom for the same reason. Our rig is wired for a second AC (50 amp service to the RV) but we chose the fan.
Deluxe Fan-Tastic Ceiling Fan Vent with Thermostat... 3 speed, draws air in or out and a thermostat.
http://www.campingworld.com/shopping/item/deluxe-fan-tastic-ceiling-fan-vent-with-thermostat/7284
It was installed by the RV shop before we picked up the RV.
It does help to cool the RV down. I would get one with the thermostat - we set it and it shuts off when the bedroom cools down and turns on when it gets warmer
To install one I think the old vent will need to be removed and the Fantastic unit installed. I you do it yourself I would purchase the tools and caulk made for working on RVs.
You should be able to get power from the ceiling lights. That is what the RV shop did on our last rig - fan power came from the bedroom light switch. On our present RV there may have been power in the "area" because we do not need the bedroom lights to be on to power up the fan.
2017 Keystone Avalanche 320RS
TV - 2011 Chevy Silverado 3500HD LTZ CCLB Duramax SRW 4X4