If you 'search' around this Forum you will find a number of discussions on the topic of fridge installation. Basically, your fridge has not been installed correctly as there should be no gaps or access from the rear of the fridge to the inside of the van. Dometic supply plates to fit at the rear of the fridge to seal these gaps and Thetford have similar devices.
What it means is that the airflow across the back of the fridge is not working as it should, and you may find the fridge does not cool as much as you would expect in hot weather. There is alos the possibility of gas fumes, if you use gas, entering the van, which is definitely not desirable.
Get your dealer to have a look and fit the fridge correctly.