How is your heat? How are you heating the Cabin? Anything you woulds change? I'm hoping good sealing and my Vetterman crossover will give me what my Wife will want in those temps.
At 10 F, the heat is reasonable. At -10 F, it is frigg'n cold! The heat into the cabin is merely "warm" with the OAT that low. We wear multiple layers of long underwear, warm socks, snow boots, etc... I wear a thin wool hat that goes under the headsets. Isaac, in the back seat, wears long hair...
Mine has a carburetor and two exhaust heat exchangers, one for the cabin and one for the carb heat. I would suggest sealing up the drafts as much as possible. Make sure that you are not getting CO into the cabin. I don't know if you need carb heat in your build, but I'd suggest as much heat exchanger for cabin heat as you can fit. ...and dress warm! A patrol has a smaller cabin to start with, so you will probably do better. Run a heat duct to the rear seat.
It also helps to block off and/or fill up the rear of the cabin as much as reasonable.