yes, put the insulation between the metal and the wood.
You can ask at your local store what would work best.
Do remember that you want to close up the between space very well, or the insulation will turn into a rodent house.
20s is NOT that cold. If you close up every opening in the winter your chickens will get frostbite and respiratory illnesses. All you need in the winter is to make sure that EITHER vents are only on one side of the building, OR all vents are up high above the head height of the chickens on perches.
Both above choices will result in no breeze at the perch, great ventilation, and healthy chickens.
For the summer you might actually WANT a breeze over the perches, because I think your area of the world is both hot and humid, a bit of a breeze would help the chickens cool off.