I used to fly a lot during winter-time some years ago. Several times I flew at temperature below 0 F. There are a couple of things to consider if you are trying to push the low temperature limit:

1) You need make sure you are warmly dressed and well protected against wind.
2) Use a transmitter mitt with a couple of hand warmers inside. Once you tried it, you can't live without it...
2) RX battery capacity will be reduced if the batteries gets cold.
3) I found I had to degrease the gear boxes of my servos in order to make them move with authority. Instead of grease I used a light oil. Check that the control linkages are moving freely when cold.
4) Nylon and/or plastic control horns and clevises get brittle at very low temperatures (do not ask how I know this). Substitute with metal parts.
5) Mix a couple of percent of gasoline in your glow fuel. This will allow the engine to run a little bit hotter than is usually the case.
6) Get a bottle of car engine "starter gas" to prime your engine before starting. It is very helpful when starting a cool engine.
7) Use a fuel with synthetic oil. If castor oil is used the engine will not turn freely if allowed to cool down.

The transmitter and its battery can often be kept fairly warm using a mitt with handwarmers, but the receiver and its battery will get cold fairly soon. Becase the electronics is usually consumer grade and not guaranteed to work below 30 F it is a good idea to test the equipment on the ground after letting it cool down to the lowest temperature you expect to fly in. Better safe than sorry...

Edit:
I forgot one important thing. If you take a very cold object inside a warm car or room there will be condensation that may cause damage (I learned this the hard way). The solution I found is as simple as it is effective, before taking your Tx inside, put it in a plastic bag and seal it while still outside. Let it warm up for a couple of hours before opening the plastic bag. In order to protect the Rx from condensation I found that the simplest solution was to put it inside a small plastic bag togheter with some small bags of moisture absorbing silica-gel.

/Red B.