Whooshing would probably be pressured side of the turbo. Only takes a small hole. There is a weak point somewhere that I've seen mentioned on here, a elbow joint that might even be plastic
While a joint is ok, I'm not sure a reputable garage would use one. By the time the joint was made a complete pipe could be installed. A pain on axle stands to get in but probably easier on a ramp.
Depending on level of security a money tin might be ok.
Leaving out of sight isn't always best as anyone who has access to the car,eg mechanics, may find it and you possibly wouldnt know straight away.
There is the option for a second lighter for the rear passenger, the cable could be there under the cubby box. You can then easily fish cable where you want it, even inside the cubby box.