I ran ATVs patrols in the desert, and I can tell you that no matter what we did, they had fine dust that took hours to clean at the end of the duty day.  The armory guys would just laugh because they knew it would take us forever to clean when we got back.

I doubt you are going overseas with your ATV, but if you are going to be in areas where there is dust or sand, try to make sure you get a quality case that has a good seal.  It will save you aggravation in the long run.