Where to best locate trans temp sender?

I want to add a transmission oil temp sender/gauge on my 92 740 turbodiesel wagon since I am pulling a 1500 GVW trailer now with it. I found that there is already a 10x11 trans. cooler mounted in front of the AC condenser coil assy. So I could easy just stick a 1/8 npt sender unit into that with some high-temp RTV. The other way would be to get a brass tee, and tee the sender into either the supply or return trans. oil line. My only concern about doing it the first way, the easy way, is that maybe with the outside air impacting directly on the trans oil cooler and sender, maybe it would read a lower temperature than actual? I believe the normal water temp for the engine is 192 deg. , should the trans oil temp never go above 200 deg also?