Here is a shot of my XP-47H project. The fuselage is vacuform, from KAE. I will be using a Revell P-47 donor kit for wings, horizontal tail, and various details. This shot shows a keel I put into vacuform models. It is 3/16 basswood. It provides a flange for easy gluing of the fuselage shells together, eliminating the need to glue the thin shells together in a butt joint, and strengthens the fuselage greatly.
The areas painted black on the keel are areas where openings like cooling vents or exhaust stacks will be placed on the outer shells, and prevents seeing the keel through these openings.