Closely related to mike pads are attenuators that let you patch a guitar amplifier's speaker output directly into a mixing console. Most guitar players I know would sooner cut off their left hand than use a direct box, and an amp pad lets you retain most of the amplifier's sound while eliminating leakage into nearby microphones. If you use 10K for both R1 resistors and 100 Ohms for R2, the pad can handle input levels up to 100 Volts before the resistors get warm. With space at a premium inside these tiny tubes, you should use the smallest components you can find. Again, Mouser and DigiKey carry these and many other electronic components.
Tantalums cost more than standard electrolytics, but they are smaller and generally higher quality.
You should use shrink-fit sleeving over all of the components or otherwise ensure that the components don't short out to one another. The S3FM comes with a plastic-coated cardboard tube that lines the inside of the case, and this prevents any wires from touching the grounded case. I recommend that you draw the schematic on a small piece of paper, and roll it up to serve as the outer insulation. To make the assembly truly secure if you don't care that it can't be opened later, you can encapsulate the whole device in potting compound. Second, it is possible that some liquid will run out the bottom while you're pouring it into the top.