Keeping the Loupe in an inside a pocket or inside your Jacket helps
For the Ground Glass - the problem with clear itself given enough time as the glass warms up with heat from your body - but in the mean time a clean cotton handkerchief for wiping away condensation and/or a mini ice scraper depending on how cold it is.
Personally, when faced with such conditions, I find it best to have the Darkcloth open at the bottom at least at first and flap the Darkcloth frequently to promote ventilation.
Misting up inside the Darkcloth can be a year round problem depending on where you like - so its important to find something that works for you
I have had no success with a snorkel - it solves the breath problem but does nothing for the warmth and perspiration coming off your body
Martin