Your electrical system is very much like mine, except I don't have the porch lights, but I do have a vent fan.
I'd say the master switch is optional, and being optional, you can put it any where you want it in the high current positive lead from the battery. The fuse, IMHO should be in the positive lead close to the battery. I have a 40 amp breaker in mine, so that is an option you can consider as well.
Calling an illegal alien an "undocumented immigrant"is like calling a drug dealer an "unlicensed pharmacist ".