This where I fitted mine
double side foam tape to hold in place. Visible to driver and passenger
Fitting the probe is another issue. I fitted mine on a rocker cover bolt, drivers side, near the engine temp sensor. If it's good enough for Mazda ... I chose here because it is away from the exhaust that has radiant as well as conductive heat and may result in a temp reading different from the engine temp.
For the wires I found a plugged hole in the LH footwell that allowed the probe through a razor slit in the rubber plug.
So far 8000Km in 10 weeks and it is working well. The only time it goes over 100C is after pulling off the freeway for whatever, probably a bongo dummy spit over having to slow down
PS you won't miss the over temp beeper