I own 5 UK's, and while the apron does blow with the wind a lot, I find the snaps will keep you modest. I have never had the kilt try blow up on me, except for the time I was on a mountain... but that's because the wind had a chance to come from underneath, which doesn't really happen often in day-to-day activities.
Maybe you could add a small bit of velcro to keep it from blowing open?