My B&M guage's instructions said to mount the sender after the cooler so that you know the cooler is working. It came with 2 T fittings, but neither matched the Nissan hard lines. I bought my own T to mount it on the rubber line and soldered a wire to the T for the sender's ground (grounds to the hard line in a "normal" installation). Thought about adding a second guage on the inlet side, just to see the high side too, just to see how effective the cooler really is. It came out of the cooler between 150 and 180 on the 2k+ mile trip I just took. I guess if it wasn't working right it would constantly get hotter on the output side.
I want to make a mount for mine in the same place as you, had my tranny guage in the mount that came with it, 3M taped to the side of the center dash in the same area, but the 3M only held for a week. I also have a digital Volt meter down there bolted to the dash where the little filler piece is for the truck E-brake.