OK, if you're going to be out in the cold for that long then exposed flesh is definitely a concern. With or without an underkilt, you should take some other precautions.

I'm just throwing out some options for kilt wearing under such conditions, though I haven't tested them:

1. Wear kilt johns and roll your hose over you knees as necessary. This allows you to roll them down when you're active or need to be presentable but cover your skin in other situations.

2. Wear long johns/running tights under your kilt and hose. Not the greatest look but you'll be warm and kilted. I know a guy who rode his bike to school every day in shorts. In the winter he wore long johns under them... even in -30C!

3. Wear your kilt low enough to cover your knees, along with the underkilt and/or kilt johns. Again, not a great look and definitely not advisable if you'll be doing a lot of walking because your kilt will rub on the back of your knees.

4. If you care for the historical look, throw on some trews or a feileadh mhor. I read somewhere that back in the day, highlanders who could afford it wore trews in the winter. Those who couldn't wrapped their plaid around themselves like a cloak.

Does anyone have field tested, successful kilt experience under the circumstances Paul is describing? 12 hours out and about, periods of activity mixed with standing, sub-zero temperature?