Direct from my Minn Kota charger manual:
MOUNTING THE CHARGER:
Due to the weight of the charger and the pounding that boats routinely endure, take the time to securely mount the charger to prevent damage.
Mounting with bolts, nuts, and washers is preferable to mounting with screws. Use the largest diameter bolts possible, and use all four mounting holes.
Your battery charger is supplied with an AC plug holder designed to hold the power cord plug when not in use. Mount the AC plug holder with four screws in a convenient dry site to prevent corrosion to the AC plug and to prevent the AC plug from making contact with the battery posts.
CAUTION – Because the body of the battery charger is metallic, do not directly mount the charger to the hull of an aluminum boat. Use a means of isolation (such as wood or plastic) to prevent the charger body as well as mounting fasteners from coming in contact with the aluminum boat structure or hull. Doing so will eliminate any risk of electrolysis that may occur when AC power is connected to the charger.