Carl,
The reason that you install a fuse in the wire close to the battery on both ends of a charging wire is that in the event of a short at any location in the circuit (plug/connector, umbilical cord, or wiring), you are protected from the fire hazard of overheated wiring. Remember that both ends of a charging circuit are connected to a battery, so fusing is required to protect against a short. I personally use 10 gauge wire and 30 amp fuses on charging circuits just incase I have a low toad battery from sitting and some recharging is necessary, but the 12 gauge wire and 20 amp fuses that Fred mentioned should be adequate.
Gerald