Tank Sensors

I get spurious readings for fresh water tank which are due to the sensors on the outside of the tank getting wet when driving.  The tape that A/S fit isn't really up to the task so I'm wondering if there's another solution? The A/S website mentions coating them in a "low viscosity coating. We use PLASTIK 70". It's a new Symbol which is still under warranty but the dealer is miles away so I was going to sort it myself as it's so trivial.

I need to buy something but this is expensive stuff, could I use anything else? Thoughts?

I suggest blobs of SIKALASTOMER-710 BUTYL SEALANT (BLACK)

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I used clear silicon sealant but I found over time it was not sticking to the tank maybe because I hadn't cleaned the tank properly.  So I pulled it off, cleaned everything up and painted some black bitumen car under-seal on the connections which I just happened to have.  I also found that the spade connections to the harness were wet through so cleaned and them up and wrapped them in self-amalgamating rubber tape.