Camp-Inn uses a 3/4" solid plywood sidewall. We have camped in ours down to about 15 degrees F. Even in the cold weather, we open the side windows slightly to vent the warm humid air to minimize the condensation. We still get some condensation on the windows and slight condensation on the sidewalls. The most important thing is that your roof is insulated, so the condensation doesn't rain on you. The Camp-Inns have foam insulation in the roofs.
Of course everybody's idea of "a little brisk" is different. Having lived in northern Minnesota, in February when it warms UP to 5 below, everybody comments that it feels good now that it isn't very cold anymore.
We don't have a heater in our teardrop, just a couple extra blankets and we have always been comfortably warm. Of course, depending on how cold it is, it helps to wear flannel nighties and a nightcap like in "The Night Before Christmas" so you aren't as tempted to stick your head under the covers. At night it takes a few minutes to warm the sheets. In the morning, close the windows for 10-15 minutes and it warms up so you can't see your breath anymore. A small DC heater would help speed this process.
Camp-Inn does offer a propane furnace for the cold blooded.
We are going to try some winter camping, in the snow, this winter.
Anybody up for a sub-zero teardrop gathering? We could ice fish, ski, sit around a BIG campfire....
Betsey