Here in Alaska, we used to pull the dust covers off so it was easier to get in there and tap the brake shoes sideways when they froze. Of course, as you say, if they are allowed to cool first there isn't generally a problem - unless you've been running through deep, loose snow, or it drifts into a wheel and freezes between the shoe and the drum before the drum cools.
While driving in the South 48 I found some discs that were stamped into a fan pattern that mounted onto the hub under the drums. These were made to blow rain water off the shoes to make the brakes effective more quickly after running in heavy rain for 100 miles or so. I found they also worked to keep snow out of the drums, as I only had one frozen brake (on a trailer - after running through an hour or so of fresh snow) after installing them on a truck in Alaska.
I always liked the "spokes" painted on the tires to see with the wheel check lights, as they caused truckers from the South 48 to scratch their heads and wonder if we weren't just a little strange.