...my parents had one on our '55 Ford station wagon, worked great when humidity was low...and the water hadn't evaporated away!
...you can sometimes see one on a car at "oldie" car shows:
...of course, it's NOT very aerodynamic! But, maybe the same idea could be "incorporated" INSIDE the body sheet metal with a NASA inlet air scoop?
...earlier post on this subject:
http://ecomodder.com/forum/119943-post16.html