I have installed two, using lexel to fill within a minicell foam perimeter glued to the hull bottoms and then slowly squeezing the transducers in.
There other methods including a more permanent glassing and/or glueing in of a pvc pipe box to the hull bottom with a cover to contain the transducer in water.
Go find a good dedicated yakfishing board and ask. You'll get some good suggestions with more details. Key trick is always to avoid air bubbles in the medium that the transducer is implanted or immersed in. The bubbles distort the feedback.
1 Canoe/Kayak Trailer
Dock & Launch Systems