[Christ]

First, if it were me, I'd look into insulating it, then something to monitor the temp back there over a few trips to get an idea of what's going on back there. (IAT sensors just give a voltage reading, and you can monitor them with a plain old multi-meter, in real time.)

If just plain insulation doesn't keep it from over cooling, even maybe then I'd look into heating the cubby that it's in with something like 15-30w heat pad or something similar.

Also, if you get under the car, you can probably see where the battery box pokes down under the chassis... if you can see it, just a simple foam box around the outside will prevent a great deal of heat loss through the windage effect (metal conducts heat to the outside air, which is moving and drawing the heat away.)