Mary years ago when we owned a different boat. We angsted over this for a year. We were advised and counseled and finally tried it by building a small dam on the hull out of RTV as an experiment.
About 4" in diameter. We put water in it and duct taped the transducer down. It worked perfectly. So then we purchased epoxy with a special attached mixer tube. Poured the epoxi in the dam. People told us absolutely no air bubbles or it would not work. The instructions said use very slow set epoxy so bubbles can leave solution prior set.
Well everything went wrong, I could see tiny air bubbles and they did not leave, the transducers ended up cocked off, and the tape did not hold.
Funny thing, we got lucky, it worked anyway, still does. Compared it with known depths to 100 ft and it is exactly on.