Parametric Mould Template generator. Enter the internal dimensions of your mould and this parametric model will generate a reusable template.
Then, just add any model file to the ‘base’ part of the mould using your slicer and print it. You can then cast a silicone mould of anything you want!

Since the model contains all parts in a single STEP file, you will have to ‘break into objects’ each piece before orienting.

Print with the orientation shown in the screenshot.

Cast your mould, then once it is set just pull the 4 pins and the mould comes apart easily, ready to be reused.

Some vaseline along the seam can sometimes help with sealing. It won't be 100% water tight without but still works pretty well.

Happy to generate custom dimensions if you don't have access to F3D