An aluminum tank is in my plan.
The level sensors rely on sensing the resistance across the 2 tank mounted sensors I think.
Covered with liquid = circuit complete, no warning lamp.
Uncovered = Circuit open, warning lamp.
They just need to be isolated from the tank body by mounting them in a grommet like the holding tank sensors.
Drill the correct size hole and deburr, insert the sensor, and tighten the first nut to expand the rubber seal, then attach your electrical connector between the first and second nut.
I like this style too...