There are also food grade silicone casting compounds, use for making chocolate molds, etc. I would think that silicone would be safe. <But the resulting object would be a bit soft & rubbery.>
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.