I have my sender in the PTO cover, within an inch from the top of the oil level (see the bung on the same side, further back). It is well protected and sees the "top oil temp" at that location.
I don't pay much attention to it empty, but loaded on a cool day it will be somewhere around 200F, and on a hot day and a big climb in the indirect gears, it will reach about 260. Obviously 5th (no gears loaded) is the coolest gear of all.
There are a few rubber grommets with little or nothing in them, and you can sneak a wire through that way.