several options here, put them on the outside, simple under a bolt on each height.
another one use a big pipe, and a smaller hose, mount the sensors on the smaller one, with centre rings to keep it in place.
cabling should be taken care off, with Pt100 best use 4 wires/sensor, 3 is also possible, even 2 is possible with a gnd wire going to each sensor.
as speed is very low you can use a switcher.
another one could be together with the level sensor on a float that sinks (used in marine to see the temperatures in the big ocean)
still another one is optical fibre, it is more expensive as a simple sensor but the results are very good.