I took the wax from the ring and kneaded the air out of it and stuck the lump to the fiberglass then pressed the transducer into it. It's important make sure you have no air bubbles and that the tranducer is level. There is another way that should work and it kind of follows the method used when epoxying it into place. That is to take a ring cut from abs pipe and glue that to the hull with resin. Then fill the ring with melted bees wax and then float the transducer on that before it hardens. A more permanent mounting is done with resin or epoxy.
The wax has worked well for me and was intended to be a temporary trial of a transom mountable transducer. That was about three years ago and it is still working. May only concern is getting wax on me when I crawl into the engine compartment or getting wax on anything stored in there. If I had to do it again I would use resin or paraffin.