I wanted to monitor the water temp at the head so I installed a brass tee in the water outlet from the intake manifold to the heater and installed the temp sensor there so it would montor water temp right out of the head...
See Attached photos
I used a short brass nipple into the manifold, a brass tee connector to the nipple, a 2 inch nipple into the center of the tee, connected the hose to the heater to this nipple and installed the temp sensor into the other "straight thru" opening in the tee.
I also replaced the heater hose with one more straight forward and added 90 degree elbows as shown in the photos.
the fittings are all standard plumbing fittings and the copper tubes are plumbing as well..