If you are building it in a shelter, have you thought about putting an old 100w light bulb lamp in it to heat it?
You can usuallly rais the temp of the wood high enough that the stuff will set.
We have also found using big halogen lamps will cure it touch dry in half an hour if we are in a hurry, or working on the inside of something. Then we will flip it over and put it over a 100w lamp for the night to finish curing
Havent tried this below -1C, but may give you some Ideas if you are in a hurry.