I was given a Coleman Thermoelectric cooler that I've had reasonably good luck with. Can use it upright like a fridge or horizontally like a cooler. Usually around $99 at the truck stops, I think. Search for Coleman Power Chill 40qt on Amazon for specs, details, and user reviews.
Supposed to keep goods 40degrees cooler than outside air. Even in Laredo, I've found it better than messing with ice and water mess. Comes with a 120v adapter too, I think, though I had to replace the one given to me with the cooler.
An important thing to remember with this cooler is to keep the fan and finned heat sink clean, which is super easy to do. It can gather a lot of dust, especially if used horizontally, that ends up looking like dryer lint, and that will reduce its capacity to pull heat from the unit.
Here's what I cleaned out of mine just last weekend. I noticed it wasn't keeping my sodas and cheese etc as cool as normal, so took it apart and cleaned it:
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All in all, at least in the way I use it, I like it a lot better than an iced cooler. I keep mine along the post where the passenger seat used to be and can access it safely while driving:
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