What you want to get installed is called a Fantastic Fan. Great way to go and you won't be sorry. The mobile RV repair folks are very familiar with these and it's an easy job for them too.
Yes, that is what you need!! I put one in the back wall of my semi, best 79 dls I ever spent! I put it in the back wall, because I did not want it on the roof for the leak factor, plus more aerodynamic! they also make a small box fan, that is 12 volt, same fan as in the vent, great addition! great products, last for ever, at least for 11 years that I know of, and I would guess they are still working with the new owner!