I've coated many species of unfinished wood down to aprox 25 degrees F. I'm sure your temperatures are much lower, so I can't guarantee if my process will work for you.

I have several  different HVLP spray outfits, that enable me to lay on thin, even coatings of finish. Thick, hand brushed coatings, will not dry well at lower temperatures. I use petroleum based polyurethane varnishes (Minwax). I first heat the varnish to about ~110 degrees F. Then it is thinned aprox 15% with acetone, and a cap full of Japan Drier is added to each quart of material being sprayed. Before shooting, stir the mixture well, until all the blushing is absorbed and the material is clear again.

Spray a light, wet, coating and let stand. The next day it will be hard to the touch, but not completely cured. At lower temperatures, this may take a couple of days. Try not to abrade the finish at this point, as permanent marks can be left.

The big box stores sell inexpensive HVLP spray outfits for aprox ~$125 and up. The worse finish with these units, is better than the best application with a brush. If you value your time, the first job will pay for an inexpensive outfit in labour costs. They work well while using petroleum and water based products. They do not have the atomization capabilities, to spray heavy bodied latex based finishes. You will need an airless outfit for that.

BOL  Gard