[jw]

Ed,
The hot new lick these days is a wet box in hull installation. Airmar, the company that makes everyones transducers got the buggs out it .
I have now experience with this install but a friend of mine install electronics for a living and say it work great eeven with the monster transducers on my big boat.
I think you would laminate a fiberglass box in the bilge area , then fill the box with mineral oil, then install the transducer.
I hope this points you in the right direction.
JW