For those who have installed this box inside either their down or seat tube, do you need to hold, tape, or wrap the box in some way so that it doesn't rattle around At all?

I wish I had. Mine is in my down tube and rattles a ton. Maybe this fall, I'll pull the bb30 adaptor out of my frame and pad the junction box or even just tape it down.

Put a thin piece of Velcro around it.

Thanks for the suggestion. I wrapped a bit of bubble wrap and electrical tape, went for a quick ride today no sound so I guess I'm good!