Insulation ideas for winter tent camping on snow?

[rainrunner]

We set up snow caves back when our boys were in scouts. I guess if we were to get there early and want to spend several days in one spot it might be worth the effort of a snow cave. But we like the ease of the tent, plus there isn't the danger of suffocation if you happen to do it wrong. If someone does decide to make one and haven't made one in the past, I would recommend a class or go with someone who knows how to make one.