Roger-
Mike brings up a good point. You should do a thorough inspection under the coach and the engine compartment. Debris of some kind may be up against an exhaust component, the surpentine belt may have problems, a hose may be displaced, or any number of other maladies, including those Mike mentioned. Could be something loose rubbing a tire, or a bad tire, or a stuck brake component.
As Karl questioned, you didn't elaborate under what circumstances you encounter the odor. It would help us to know that.
Joel