Some are - but a lot aren't. If there's an upper & lower vent on the wall of the van the important bits (jet / burner / flue) can be serviced. Quite a number of vans have the lower vent via the floor preventing any useful access to the lower rear of the fridge without removal. In an ideal world, IMO, all fridge connections would be on the rear, a seal-fixing flange would exist all the way round the rear of the appliance, and a full height locker-style door would incorporate the vents. Anything else is simply lazy, lack-of-competition, design & manufacture.One of the main reasons I have a habitation service done is / was the fridge service to remove some of the risk of CO poisoning, then similar for heater. I thought all the fridge workings were accessed via a vent on the outside, ours is, or appears to be