Its sticks really well for not being permanent. I have had my kayak in the 100 degree heat and stored it upside down it has not budged.
Right I'm more worried about the signal strength. Seems like the signal would penetrate it less effectively than goop.
But I mean since it's not permanent, I could do this tonight for this weekend and then switch to goop next week if I wanted to. Or, eventually I might install a track system and side-mount it, so having a non-permanent install for now would be nice. And the only hole I'll need to drill will remain regardless since my head unit will be in the same spot either way...
Might give this a shot. About how thick should I make the putty under the transducer? And bring it up around the edges of the transducer?