The original module has two significant shotcomings: a rather short maximum decay time and no decay at all if the potmeter is turned all the way down.. The first problem is solved by using a larger capacitor (here: 330 uF) and the second issue by putting a 220 Ohm resistor in series with the potmeter to prevent resistance dropping to zero.

Layout on a small 10x10 hole PCB. The potmeter is not soldered to the circuit board but hooked up with wires so the entire module can be mounted on a panel. I'm using a 1N4007 diode here but any "standard" diode will probably do.

RED: TRIGGER IN BLACK: GND WHITE: EG OUT