Gil, My preference is the classic card stock method. To me, the 'filler' method is fine for a one-off model. The paper method requires quite a bit more effort to design, but I think is more accessible to modelers (assuming that you are sharing this model). With that said though, the filler method could also be accomplished using tissue paper rather than filler. This would probably be the fastest way to see if the hull formers are designed correctly.