Can't plug it in, just they way they are built, it is an off road model which could be why. (Ours is the Johnno's Off Road tourer if you want to look it up. We swapped the kitchen for the one on the Evolution.)
The fridge itself can be plugged in. The batteries just run the fridge and LED lights. We can also charge phones, tablets etc. I power needs are quite low. All the cooking is on gas. We also have a secondary battery in the 4wd if need be. This is isolated so we don't drain the main battery.

I did see you can now get sleepout/tent attachments for shade tents. Looked really interesting. If we did not have the camper trailer, it is something we would consider for camping.