[Terryd]

A fuse is the fastest acting protective device in any case. A breaker has the convenience of being resettable but won't open as fast as a fuse will.
Put a disconnect switch at the battery and a main fuse after. The main fuse should be sized based on the size of your wire or cable. I keep a spare fuse in the car. The purpose of any protective device is to protect the WIRE. You can take an inline fuse holder with a 5 amp fuse and connect it across your main switch terminals. This will give you memory power for your electronics. When the main switch is in the open position the power will travel through the "memory" fuse. Just remember that fuse is in there if you want to remove power completely to the system for service. If you forget to turn the main switch on and try to use anything with an amp draw over 5 amps the memory fuse will blow. Also handy for anti theft as you can kill the main power but still have power for an alarm. If the thief gets in they won't be able to crank unless they find your main switch.