Cooler MT Temp Probe Question

Guys,
I need to find a way to insert a probe into my cooler MT. I can simply hang it over the top, but the lid will crimp the lead. I am not too keen on drilling another hole into the side either. My reason is I want to know what the temp is inside the MT before going through the recirc pump and back to the top of the MT. Is it possible to use something like this with the probe instead of the thermometer without leaking?:


I have another question:
I see most RIMS tubes with a temp probe inserted. Why is it done that way? It seems to me that the temp inside the MT is what matters. If that temp needs to be increased the RIMS heater turns on to heat the recirculating wort. I'm sure there is an obvious reason and someone will clear that up quickly.

I measure both in the grain bed and in line between MT ball valve and pump. I use a thermometer in stainless T just as you've posted. Not leaks, it works great.

I bought a Tee and a compression fitting which I believe is what holds the thermometer in place in the picture above. I think I need a gasket or an o-ring or something to seal it. I'll be using a thermoprobe that goes to my PID. Can someone advise me on what I need to make this leak proof?