Just out of curiosity is the external walls below the eaves insulated and also the between the floor joists to the walls of the cupboards. If not you will get what is called cold bridging. When i insulate the combs I will put the solid insulation like cellotex or kingspan leaving a 50mm air cap. Then I would then cover the bottom side of the rafter with a 25mm insulation like cellotex again marking the rafters for fixing the plasterboard to. The second layer of insulation is to stop cold bridging from the rafters Before fixing the plasterboard I would tape all the joints with a foil tape so I have VCL. There is other ways like using multi foils or insulated plasterboard and verandering the combs after the insulation to produce a service chanel. For the cases to run so the insulation has no breaks. In the mean time just insulate the door and place self adhesive foam on the door stops that will seal the door into the the cupboards
