May I interject some points here that come from my cold weather survival schools?

There are five places on your body which you MUST keep warm for the rest of you to feel warm.

In order of priority they are;
1) The top of your head.
2) A trangular area of your back with two points at your shoulders and the third at the base of your spine.
3) The backs of your hands.
4) The tops of your feet.
5) Your nose.

Notice that nowhere does it mention your willie. Look in old pictures and you will see people in very extreme conditions with other parts of their bodies uncovered, but the above, and able to function.

Dress in a hat, a good jacket, a pair of gloves and a pair of dry boots with thick socks and willie and the boys will feel snug and comfy.

It's not about those conditions of the artic in January when any exposed skin is dangerous, but for normal cold and snow, keeping the vital areas warm will do very nicely.

MUG's have been worn for millenia, and in some pretty harsh conditions. If willie feels cold, cover the other part of your body that is actually cold, and willie will thank you.
I am working on an anti-chafe/hygiene add on to my kilts, that started with Riverkilt's fire helmet chafe post, and will have some photos in about a week. But to keep warm look at old pictures of Highlanders, and follow the example.