[flyingsherpa]

I wouldn't draw down the 12V 50% on a regular basis (27Ah out of 60), but you might be able to get away with it for occasional use. You could also remote start the car twice during the day, which should top off the 12V (and cool the cabin / traction battery in crazy AZ heat).

More fun would be to get a 100W solar panel stored in the back hooked directly up to the cooler. When parked at work, pull the panel out and position (roof rack?) for optimal power. Actually, I think there are smaller panels (10-30W-ish?) that you could keep mounted inside the car and use to trickle charge the 12V while your cooler draws from it. Might actually work.

 

[flyingsherpa]

Does your 5th Wheel have grid power and its own fridge? If so, is this whole effort just to take home your leftover weekly groceries from the 5th Wheel? Can't you just leave them there for a few days? Just trying to figure out the motivation behind this (though I think it could be a technically neat project with fun toys).

Convince your jobsite that they need a VIA truck to power some tools, and you can leave your cooler plugged into it all day