This is a 3d printed mold generator, just insert any .STL file and follow the instructions.
Download the .scad file and follow the instructions. The Customizer is only for the thing to be shown at the "Customizable"
I replaced the original mold generator with a fixed version.
Use some coats of filler and sand, do it 3-5 times. this will help to remove the layer lines. spray some Mold Release.
Use clamps to clamp the two parts together and then you can warp it with masking tape so no liquid will drop out.
Release your model.