@keithellis Lovely idea.
I've followed suit and knocked up one but with the sensor facing the other way, so that it faces the meter, and the preset pot is and LEDs are facing away from the meter.

That way the sensor side of the case can be stuck to the face of the meter, and the pot adjusted without removing it from the meter. The flashing light on DO flashes in sync with the LED on the meter. Theres a little ring that holds the sensor flush with the face of the case so it can lie flat on the front of the meter.

Also, its a good idea to use black / dark coloured PLA so as to block out the any stray light that may illuminate the sensor (such as when the meter man comes to read it and shines a bright torch to see the dials).