Seacraft Hull Construction & mounting transducer

[hedgehog1957]

I just recently bought a 1978 Scepter, and picked up a Garmmin 178C Fishfinder/GPS. I need to mount the transducer and would prefer not to use transom mount. Garmin says that if hull does not contain core (wood or foam), and thickness of hull is less than 1" thick, I can use "shoot-thru-hull" and mount in hull rather than drilling holes in transom. Can someone help me out with the hull contruction, and make any recomendations? Thanks.