You didn't mention what Teensy you have, or whether you want to use the USB port for just power, or whether you want to use it for programming the Teensy. If you don't need to program the Teensy while it is in the box or use the USB for input/output, you could just solder the +/- connections of a panel mount USB to the ground and VUSB connection. Note on Teensy 3.2, 3.5, and 3.6, you would need to use the ground pin next to pin 0 and not the analog ground pin between VIN and 3.3v. On the Teensy LC, 4.0, and 4.1, you can use that pin, since those Teensys don't have a separate analog ground pin.
If you have a Teensy 4.0, that does not have the D-/D+ USB pins exposed on the bottom of the PCB (the D-/D+ pins are for the secondary USB host controller). For the Teensy 4.0, you would need to construct something that goes from the panel mount housing to the micro USB-B on the Teensy.
Adafruit has a series of USB DIY parts that use a standard flat ribbon cable so you can build your own connection:
https://www.adafruit.com/?q=DIY USB Cable Parts
If you have a Teensy 3.2, you could use this PCB:
https://github.com/macaba/Teensy-3.2-USB
One concern about any form of panel jack is how secure it is for repeated attachments and removal of the USB cable. The boards that kd5rxt-mark posted would work, but they might not attach solidly to the box. It sort of depends how finished you want your box to be.
Another way to solve the problem is to construct your box so that the Teensy's micro USB-B connector is flush with the wall. Obviously you would need to mount the Teensy on a PCB that solidly connects to the base of your box.