I was faced with such dilemmas when I lived in Chicago, and it'd be 15-20 degrees outside. But I had a 2-car brick garage, and a propane fired bullet heater.
I knew well not to run such a heater continuously due to noxious fumes- carbon monoxide poisoning, and exhausting oxygen, but could be run intermittedly for short periods, where it would warm the garage and vehicle, and would also help aid the waxes like Collinite set up better for removal.
If no garage to use, maybe you could find a relative or friend that does, who would let you use such on a rare occasion, just to do a wipe down, and a wax? Just be very careful if using portable heaters to aid you. They can be extremely dangerous as both a fire hazard, and as well the poisonous effects.
Such a possible arrangement could be a win-win situation, where over a weekend you can possibly do both of your vehicles?