recommedation for ultrasonic water level sensor?

So you're going with your $100 solution instead of my $10 solution? :wink:

For a load cell subjected to the elements I'd worry about UV degradation of the wires/strain gauges and oxidation of the typically aluminum bar they are mounted on (especially due to galvanic corrosion if mounted to steel). Kept protected from moisture/light and not overloaded, though, it should last a long time.