Some basic mold boxes for molding single buttons,
Tinkercad files here:
My design goal with this was to provide enough room so the walls don't bow but also produce small and practical molds for gamecube controller buttons. I have not used these yet (as my giant gang molds are still working fine) but intend to form a mold with them soon and I'll get some pictures up. The raised area provides a place to hot glue or superglue your OEM button down, and then pour the silicone over. (I highly recommend smooth-on mold start 30 as a starter silicone, oomoo is often recommended but the molds just won't last long) The corners of these raised edges are a good place to drill or cut your sprue holes, and the keying and raised platforms should help prevent flash and allow you to squish the mold sealed very easily.
After you've done this and cured the silicone, pull the silicone out, seat the buttons firmly back in place, put the mold back in "upside down" and wrap tape (duct tape works well) and a rubber band around the mold's walls - then pour in the top half of the silicone mold. For more information on the mold making process - check out http://customg.cc/ and join the custom gamecube discord - we're friendly and we have a lot of information available :)