Hi,
I’d like to measure water temperature in lake and be able to read it in VRM. Could it be done by installing a sensor for GX devices under water and connecting it to Ekrano GX?
Theoretically yes you could do this. However, I doubt that the Victron sensor is suitable for immersion into water in terms of water ingress. You could insert it into what is called a thermowell, a closed ended pipe that dips into the lake with the sensor inside the tube. The sensor sits in the air inside the tube so does not get wet. This means water temperature changes are slightly damped due to needing t o transfer heat through the thermowell.
Another thought is making your own sensor which wall be smaller so you need a smaller thermowell or you may be able to encapsulate it better to make it waterproof. See linked post to get info on making your own.