Maybe you should spray paint the inside with a rubber coat for better short circuit protection?
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If you're planning on giving them away. Go on ebay and get like some cool altoids tins that fit their style. Maybe some vintage.
VV/V/W, I don't know if you checked the price tags on the chips. The LM2596S DC-DC Step Down module is a easy install and cheap. 1/2" thickness. You could also do a mini voltage display. That combo is about $7. You could do the Vamo chips from Fasttech for $11 a pop. There also the OKLA chips, seem thin, never used them though.