Ruggedizing a component for extended temperature
We had to warm up an enclosure for this very reason.  We ended up using a heater such as this one.  There are many of these; try searching for "Enclosure Heaters".  Most 24VDC heaters will run on 28V; make sure you check the spec sheets.

If the heater doesn't come with a thermostat, this one is good and relatively inexpensive.  Set its trip point down to near-freezing.

As far as determining how much wattage you need, it depends on the area of exposed surface, the lowest ambient temp it may see, and the material of the enclosure.  I believe that there are online calculators for this, although in my company the mechanical engineers figured out that part :)

Good luck!