Back to Paul the dipschidt now.
I rigged a fishfinder on mine last week. I hope to try it out tomorrow.
A transducer will shoot beautifully through the hull of a rotomolded kayak. A bed of medium duty silicone serves as the attachment point between the hull and transducer. It must be free of air bubbles. A kneeling mat serves as the battery (12V deer feeder type) holder. It is held down with the same medium duty silicone.