I have a 60 lt evacool in the ute which never gets turned off. We usually do enough driving to keep the batteries charged, and have an 80w panel - however chilling hot tinnies in the freezer section drags a bit more power out of it - go figure.
We also have a cheap ($350 companion 33 litre) 3 way for extended trips up the beach in the one place - set it up and leave it. It also means the girls have a fridge with the necessities while the ute is away (maybe fishing or something?).
I'd strongly recommend a chest type fridge/freezer over a front opening bar fridge simply because the cool air can't 'fall out'.
I've tried the chest freezer/genny thing as well - once - and it drove me nuts. Good luck, but in the end there isn't a viable cheap alternative to purpose built refrigeration.