To minimize moisture formation on the mobo when subzero, place the mobo in a bin and displace all the air with a gas like Sulphur Hexaflouride. This gas is heavier than air and will thus displace any air around the mobo. It is also an electrical insulator and is used for arcing protection on high voltage systems.
If acquiring and using the gas is hard, it might be an opportunity to seek a collaboration with fellow Canadian chemistry Youtuber, NileRed.