Quote from ARB website:- ARB fridges have a durable external case which is powder coated, robust zinc steel which is designed to withstand extreme off road conditions.
I personally think the ARB fridge would suffer if stored out in the elements, such as in the back of an uncovered ute tray, however saying this, I have a friend with Bushman fridge which has spent a fair share of its life in the back of a ute, and which is similar construction as the ARB fridges, and it is still going strong.
I've also owned a 60 ltr Trailblazer fridge as well as an Autofridge, and whilst the Trailblazer is probably the most robust fridge you could buy, and would survive anything you could throw at it, the ARB fridge has the most user friendly features.
Here is a link which I discovered when I was doing my research prior to buying an ARB 47ltr fridge and was found on the "My FJ Cruiser Forum". It gives you a good look at the fridge and its features compared to the old ARB/Engel models. But remember this is only one persons views on the fridge also, but a good insight.
The New ARB Fridge Freezer