Here’s a quick video that demonstrates the installation and use of a moisture quilt for winter insulation and ventilation.
All of my moisture quilts are built differently because I’ve never put much planning into building them (I have zero woodworking skills). Some are converted ventilation rims that require a rim underneath, like the one in this video. Others have built in rims as part of the design. Some fit perfectly and create a tight seal on the bottom. Some don’t. And it doesn’t seem to matter either way because they all do a great job at wicking moisture out of the hives and keeping my bees dry all winter.
Moisture quilts, in my experience, aren’t necessary in local climates that aren’t particularly damp and foggy and wet. Smaller colonies that don’t produce much condensation from the bees’ respiration don’t always need extra ventilation or insulation either. A piece of hard insulation over the inner cover often does the trick. Moisture quilts can be a bit scary, too, when it seems like half the colony on warm days attaches itself to the bottom screen of the quilt. But for me the pros outweigh the cons. If dampness is a problem inside any of my hives, I know a moisture quilt will fix it.
Empty moisture quilts are excellent ventilation aids in the summer too.