Take a look at the pics in my Webshot link in my signature. I think the pics are in my "modifications" folder.
I put my sender in the pan...passenger side, towards the front. All I did was drill a hole, tap it (which only gave me 2 or 3 threads), thread the sender in, and JB Weld around it. Never had a leak.
Oh, and I put it in the pan because I feel that's the best place. That's the temperature of the fluid that will be running INTO the inner-workings of the tranny. The cooler line out of the tranny is at the temp after it gets heated up by the torque converter, etc. The cooler line into the tranny tells you what the temp going into the pan is, but that just heats up as it sits in the pan. The pressure port is not a good place to use, in my opinion.