Need a little help with my circuit schematic for a DIY project of mine

So this circuit is a 12V to 5V regulated voltage circuit with a usb alternate power source as well as data pass through connection (confusing, to me not really, just ask if you need more clarification) and in order for the regulator part to work (the L7805CV date sheet regulator - I know its inefficient, just its what I have) it requires a connection to ground. This circuit is going inside a project enclosure so its A) looks nice and B) better portability. I have NO IDEA where i put ground in the project enclosure (which will be custom made of like laser cut plastic or something, haven't decided yet) I thought maybe someone on here could help? Thanks.