A method of sealing an opening in a bulkhead with a fitting assembly having a tube, a mounting flange, a thermal shell, an adapter, a bushing, and a jam nut may include inserting the tube through the opening; placing the mounting flange against the bulkhead, the mounting flange attached to the thermal shell, the thermal shell attached to the tube, and the mounting flange attached to the adapter so that the adapter extends away from the mounting flange and from the thermal shell through the opening; forming an air pocket by spacing a portion of the thermal shell away from the tube; placing the bushing on the adapter; and tightening the jam nut on the adapter to sandwich the bulkhead between the mounting flange and the bushing to form a seal between the mounting flange and the bushing to seal the opening.