Yamaha do a top rack that allows yor should allow a plate for a top box to be added or you can fabricate a small plate to allow a top box to be added.

As for the pannier racks, if your only going to ever be using soft luggage why not make your own pannier racks or a simple 2-3 bars alot the side to just stop the panniers from folding in.

I had this idea but ended up making a proper rack and buying my self some alpo tin boxs as it near worked out as cheap as getting a rack and soft luggage all in.

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Plough on