here is another option if you want flashy, look at most any real computer store, and get a hardware monitor, will give you a digital readout of usually upto 5 thermal probes ( included) has 12 volt DC output and adjustable set points to turn fan on and off inside a computer, even vary speed if desired, again most have 5 inputs and outputs, just check the ratings, the better units will support upto 1.5 amps at 12 volt per output, and todays muffin fans for PC's are quiet and small sized with amazing airflow.

the only quirk I see to this plan, they want 12 volts IN, not the 13.8, so may have to tweak the input voltage a little to get it to play nice with the onboard power.

Yea I know, I never said it would be a drop in,but it would give a nice display to actually monitor the radio stacks/ glass panels yada yada. and you can get probes upto 5 feet long very easily.