I know Richard has already ordered a Givi Monokey topcase hardware kit to use his Givi top case (?E460 that he had recently bought and mounted to the VFR) on the BMW. Since the raffle bike came with the BMW saddlebag mounting hardware that may make theirs a better option, instead of buying new mounting hardware (and possible removing the BMW stuff). But I'm sure he'll look for a good deal on any and all saddle bags that might work. Maybe if he goes with a different option than BMW that mounting hardware can be removed and sold.
All that will beat the last minute luggage setup we used to get home from STAR in VT, which was strapping his duffel like dry bag and tank bag to the back seat and rack, while moving other stuff of his into my bags and using the Givi top case liner as an additional bag on the back seat of my Sprint (adding to a full set of top case and saddle bag). Good thing we both had various bungee cords to use.
My experience with bag liners was model specific ones (especially for European bikes like my Triumph Sprint) were pretty expensive, so I found something close and they've worked well. RKA (to me anyway) = premium price for a product that has declined in quality. Having to pay for a raincover that barely stops a light mist from making the tank bag wet seems pretty unreasonable.
Yes, BMW stuff is expensive, I think he learned that getting first service done where an oil change was over $200. (But then I think all of us who do those at home would find them to be very expensive at a dealer, especially if you don't use the high priced OEM oil and filters.)