Only time I found it somewhat effective was when I put frozen ice packs in it after cooling it down inside first. Then it kept beer and soda ice cold all day.
So with ice packs it will keep things cool like a regular cooler I assume. You are talking about after it is unplugged? I can see cooling it before hand, getting in the truck and driving with it on. Then taking it out to fish some, return and turn it back on. How would it work in this scenario.
We usually boondock more than anything, but our fridge is small in the TT so when at hookups it would be nice.
I have already thought of some hilarious scenario's, with a generator.