A smell when you drive is usually caused by lack of water in the P-traps (sinks, shower, etc) or a defective anti-siphon valves (that pipe under the sink with a funny looking cap on it). Either will allow odors to come back into the coach. One of those scavenger vents may help move air away from the interior, but the right fix is to eliminate the path the odor takes to get into the rig in the first place.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL