A habitation check / service is a check on all the parts of the coach as apposed to a chassis service which is the servicing of the chassis, and mechanicals.
A habitation check will (or should) include things like a damp check to ensure that there is no water ingress a test of the electrical systems and gas systems, functional tests of all appliances etc.
For instance the flues on heaters and boilers and fridges need to be cleaned out periodically. Thermostats need to be checked to make sure that they are working ok, and also the gas ignitors need to be checked / adjusted so that the appliance will actually light.......
The entrance step and slide outs should also be checked for correct operation and alignment at the same time.
Stuff like that should be included in a habitation check