First off (this is just my opinion) I would take my kayak to OEX SSB (the nearest to me and familiar with Andy's work
) and while there also check with him get his input or just have him change the transducer around and mount on the inside for a "wet mount" and seal the holes.
If I decided to leave it on the bottom, I might think about replacing the screws with
bolts & well nuts for break away purposes in case it catches on rocks or other obstacles while launching/landing.
Or you could leave it on the outside and worry about tearing off the transducer or damaging it or (cracking) your kayak if your transducer hits something while launching/landing or just cruising around, also worrying about having a fish dive under your kayak and wrapping around it.
Just my .02
FFY
