Hear me out! Recent wood prices have been crazy and some old-growth wood (like Sitka spruce) is just not sustainable in the long run, it will simply run out because there is far more demand than supply. On the other hand, some plywood including aircraft-grade Finnish birch is made from sustainably-managed forests so you can be more confident in a steady supply at a reasonable price for many years to come. So, what about molded (or moulded as they would have said at de Havilland's) plywood like a Mosquito for a small homebuilt? Check out the construction section of this clip from about 3:40 to 5:12. Note that there is no second female mold or vacuum bag or anything like that over the mold, just steel straps to hold everything in place.
Now I am not suggesting that concrete molds are the way to go, but I think it would be possible to do a male plug for a fuselage in a simpler way, maybe precut plywood frames that the builder stands on a workbench with foam blocks between them and then cuts or hot-wires the foam away. Builders could even share plugs or give them to another builder. You could probably get away with identical left/right or top/bottom fuselage shells made from a single plug. Instead of spruce longerons you'd have a mostly monocoque structure with more layers of plywood where the stresses are high and fewer where they are low. It could make a light, strong, and beautiful structure. Just look at the fuselage of the Loughead (later Lockheed) S-1 Sport of 1920. Now imagine a similar fuselage with a bubble canopy, fully-faired engine, and monoplane wing.
Now I am not suggesting that concrete molds are the way to go, but I think it would be possible to do a male plug for a fuselage in a simpler way, maybe precut plywood frames that the builder stands on a workbench with foam blocks between them and then cuts or hot-wires the foam away. Builders could even share plugs or give them to another builder. You could probably get away with identical left/right or top/bottom fuselage shells made from a single plug. Instead of spruce longerons you'd have a mostly monocoque structure with more layers of plywood where the stresses are high and fewer where they are low. It could make a light, strong, and beautiful structure. Just look at the fuselage of the Loughead (later Lockheed) S-1 Sport of 1920. Now imagine a similar fuselage with a bubble canopy, fully-faired engine, and monoplane wing.