Polyester gets brittle - epoxy shouldn't.
The transducers are potted in epoxy - nothing will have an effect on it.
That is the beauty of attaching the transducer to the hull with whatever you choose instead of a liquid filled tube - nothing to leak.
The instructions state that epoxy is too brittle. Here are the Warnings within the Installation Instructions.
: Always wear safety goggles and a dust
mask to avoid personal injury.
: The fiberglass hull below the transducer
must be solid. The transducer
will not transmit through
coring material such as foam or balsa wood.
: Do not use an epoxy adhesive because it
is too brittle.
: Never pull, carry, or hold the transducer by
the cable. This may sever internal connections.
: Never use solvents. Cleaners, fuel,
sealants, paint, and other
products may contain strong
solvents, such as acetone, which attack many
plastics, greatly reducing their strength.
: Please read the inst
before proceeding with the installation. These
instructions supersede any ot
her instructions in your
instrument manual if they differ