Replacement crystal on Uno for cold temperatures
There is a solution for just this problem, it's a "crystal oven". It is used to keep a crystal at a constant temperature so that the oscillating ferquency remains very stable.

Crystal ovens are usually expensive as they are quite precise and have good insultaion, but here's a kit that you might adapt for your uses: http://www.minikits.com.au/Oscillator-Heater, or google around to see if you find something that might suit you better.

You could also consider making a heater with a simple temperature regulator of your own to keep the crystal warm  (many temperature sensors for Arduino are available on the web).