The fuse is to protect the wiring and it is a dead cert that the inverter's fuse will be way too big to protect the cable coming from the MPPT, so that will require its own fuse. You can connect the MPPT cables directly to the batteries (via that fuse, but keep it outside of the battery box), or to the battery side of the isolation switch, or if it's more convenient, to the DC connections on the Combi. Electrically they're all the same, and any of them will comply with the BSS.
Certainly not a 'requirement', and they make the alternator work a lot harder than it's probably designed to do. Nevertheless it's an option. What alternator do you have?