I recently found these great articles by Jan Mrázek on his silicone casting process ([1], [2]). He's using a resin printer to print the molds, as well as the rigid cores that he casts the silicon over. He's also developed a process for injecting the silicone into the mold, using cheap and available tools. Good stuff!
If you own an Elegoo Saturn, also check out the casted cleaning kit he sells.