I know I'm replying a little late, but if clown white is applied the right way, it shouldn't go anywhere EVER (my cast mates and I used Ben Nye through a 20 show run of "Oh, What A Lovely War" and didn't have one incident of it bleeding on our costumes). It should be patted down with baby powder or cornstarch (works just like setting powder) to keep it from going where it's not supposed to. It can get a little uncomfortable because it doesn't breathe very well, but sometimes that's just the price we have to pay as lovely, lovely models.
I don't know that I'd use a waterbased makeup if you're going to be wearing this at Comic Con. Waterbased will stain and get everywhere if you touch it while you're sweating. :/ Plus, having to excuse yourself to go reapply throughout the day is no fun.