Way to make custom shells safely?

Hello, an obsession with Another Crabs Treasure has led me to research hermit crabs as pets. I have been looking up ways to make a custom shell, but unfortunately most methods seem very unsafe for hermit crabs. I was wondering if there are any suggestions or ideas for a custom shell, and I wanted to propose an idea and see how safe it might be. Don't worry, I'm not going to impulse-buy a pet just because of a hyperfixation. I am doing lots of research and I will not purchase anything until I have an adequate enclosure.

I figured I could 3D print a design and maybe create a mold out of food-safe silicone, and then find a material that is safe for crabs to ingest incase they break apart the shell. I do not know if such a material exists, though. Of course, this is a lot of work to go through for a crab to possibly decide it's a better decoration ore snack. Thoughts?