Solder these four wires to a new Pro Trinket (without header pins installed) according to the circuit diagram and trim off the excess wire with flush snips. Likewise attach the optional switch and/or vibration sensor.
Tin the (-) and (+) pads on the back of your Pro Trinket, then solder the wires from the battery holder to them.
Use a dab of E6000 to protect these solder joints and also provide some strain relief to the wires.
Turn on the circuit to check it works, and if it does, it’s time to waterproof the circuit. Encase the Trinket in heat shrink tubing or glue, or spray conformal coating. Use Permatex 66B silicone adhesive to plug the open ends of LED strip, and watch this video for more tips on ruggedizing your projects: