I'm sharing a serial gateway I built, based on the Easy-Peasy Serial Gateway.
You can find the hardware on OpenHardware: Easy-Peasy-LEDsy MySensors NRF24 Serial Gateway. It is basically a D1 mini with a shield into which you connect an nRF24+PA+LNA module and the LEDs.

Here are the stl files:
GW_Case.stl
GW_Cover.stl
GW_Hold Down.stl

It has a snap on cover, ventilation, and a hold-down to fix the D1 mini.