I used 1/16" and worked great wet it from outside and it bends easy, be patient and apply force gradually Instead of adding two 3" sheets have a 3" at the center and two 1.5" sheeting to its sides this way you will have the joints on the sides, beacuse of CA this will be hard to bend and you will have a better curvature at top. You can see this on pictures.

Also make sure that you sand down the formers 1/16" so that the balsa sheeting will flush with the fuse sides.