Residential-type turbine attic fan --> to an RV?

Anyone ever thought of, used, or has seen an RV roof vent/fan styled like the turbine attic fans you put in house attics? I was just pondering on life and such, and thought that if you could mount a suitably-sized fan on the roof, it would help exhaust warm air on those days when running the AC just isn't kosher, and even when stopped, the wind would move it enough to pull air out of the RV/trailer, negating the need to use the DC vent fans many of us have. One might have to work up some sort of locking mechanism, so as not to suck the cat up out of the thing when you're doing 80 MPH or so, but I would think a small, 6- to 10-inch diameter turbine might be quite a possibility.

Engineers and/or more wise and worldly listeners are welcome to debunk this theory. What am I not considering?

:)