Offered not as a recommendation, but as a reference to another alternative.
I've got an old Standard Horizon depth finder with what looks like a transom mount transducer. Some prior owner cut a hole in the head sole and put it there with what appears to be silicon sealant. The hole is covered by the cut-out. It works, when I'm paying attention.
(I keep looking at that hole and think about shower drain possibilities.)
Charlie Lincoln • Cathlamet, WA • Islander 28 #108