Funny - I've never seen a pair on a vehicle down here... It's a great idea, though, and the website might attract some more attention if the nuts weren't photoshopped in on the pictures...
Have any of you seen that portaloo that you fix to the bumper of your car? I'll have to find some pics for those of you who haven't cos its so fucking stupid when you can just piss on a tree, bush, squirrel, family friend etc.