Propane volume detection

Sounds like a fun project.
Initially I'm trying to put something together that would notify the level of the propane tank when it goes under 30% or so.

got a relative that can't get out to check the tank and I can't drive to check it for them.

the tankutility device kinda already does it.. but they want 200$ for a Hall effect sensor and some simple programming.

figured I would try this first.
finding the correct sensor is the first thing.. it is already made.. but sounds like Rochester is holding it under lock and key