when i did mine nearly 20yrs ago i ran a seperate fused cable to feed just the fuse box, and a second larger cable to the starter via a mini starter solonoid. meaning the starter cable was only powered whilst cranking. i hid a button under the steering cowl to the mini solonoid and the key still operated the starter.
i did it this way because i had loads of old stereo shit left over, and i was skint.

have you thought about a circuit breaker rather than a fuse. less hassle if its needed.