I'd use heat shrink tubing on all the solder joints and over the capacitor as well. Electrical tape works but it gets less sticky over time and will eventually start to come unwrapped and you'll fry another decoder somewhere down the line. The capacitor with the Soundbug is so big that it's hard to find a place to stick it. Covering that with heat shrink tubing will allow you to place it wherever you have room without worrying about any of the metal parts touching the frame. I'm assuming that, since you're using the DH165A0 decoder, that you are replacing the existing light control board on the MP15. The engine should be DCC ready but it's always a good idea to check for continuity between the frame and motor to make sure the motor is really isolated form the frame.
