Thermo-electric coolers (Coleman, Koolatron, etc) and batteries

They only cool down about 30 or 40 degrees ambient temperature.
So if it is 90 degrees in your truck, the cooler will be 50 or 60 degrees.
They don’t draw a lot of power, so on a 10 hour rest you would be fine. On a 34 hour break you may want to start the truck once or twice.

 

Koolatron has one with what they call heat pipe technology. Cools even better than that...

 

Yup, that's about right.
Except there are way better quality ones such as Engel or ARB. They cost over $600 and up.
They look like a regular cooler, but they have an actual compressor in them and can even be dialed down to below freezing.

 

Not really. Keep in mind that they have pretty decent insulation and if they are pretty full they don't heat up that quickly.

I never left mine running while I was out of the truck for more than a few minutes. They all (at least the cheaper ones, such as you find for 100-200 bucks at a truck stop or walmart) seem to have issues with the plugs heating up. I had more than a few plugs melt on me and I didn't want that happening while I was out of the truck and starting a fire.

If you are out of the truck for a day, throw some ice in there, or bring it in the house with you if you are going home. It's just as effective as any other cheap insulated cooler without being powered on.