The instructions with the fridge show the minimum air space at the back, bottom and top of the fridge. The void is ventilated by convection.
On my van I have a Dometic CRX50, there is a small gap under the fridge, a void behind the fridge and there is a gap of approx 10mm between the worktop and the side of the van.
In my case I removed the fridge after 4 years use on and off, while it was removed I cleaned out a fairly light coating of dust, evidence that convection is active.
It’s pretty important that the skin of the van body is well insulated behind the fridge otherwise the sun will heat this void.