I like many others on this forum, I was quite embarrassed about the Sea Ray QUACK QUACK horn, so I found this horn on ebay after searching many options including many good ideas in other posts on this forum.
It is very loud, I did a bench test and it left my ears ringing, its actually a mini...
I made a new one out of timber just like many others have done on this forum, looks more stylish in my own opinion. Also the plastic ones always seem to crack just like what happened to mine in the first photo.
Have you thought of just epoxying your transducer on to the inside of the hull, say in the engine bay. All transducers will penitrate through fibreglass hulls with no issues. the only loss is water temp, that is, if your transducer has this option.
I have done this to many boats, best part, no...