Learn the proper way to install accessories in cored hulls and decks. Whether you are adding a transducer, an antenna; replacing a hatch; or repairing a bowrail stanchion, the procedure for cutting and drilling holes in cored laminate are more complex than the techniques that apply to solid fiberglass. Basically, the cutout must be sealed as well as sealing the fitting
Pull through-hull fittings, engine mounting bolts and other penetrations on a periodic basis in order to inspect the core and make sure water is not getting in.
Reseal fittings and fixtures regularly. We can't give you a specific time frame for this, because different caulks and different environmental conditions, result in the need to re-seal or re-caulk at different rates. Bottom line, caulk isn't forever, so pull and reseal fuel fittings, engine bolts, antenna mounts, rail stanchions.....any fitting that passes through or into the core or that is fastened through or into the core---needs to be resealed regularly.
Buy a moisture meter and use it if you have a cored hull. These can be had for as little as $250. Of course, if you don't want to buy a meter and learn how to use it, you can always hire a marine surveyor to check your boat's core material for moisture periodically.