Quick to remove, lightweight, waterproof (and already has about 8,000 touring miles on it)
Dowco overnight bag (sprayed with waterproofing) around $50, mounting straps included.
Yamaha Star rear luggage rack: $145.35
The Dowco bags are rugged and they've adapted to my VT1100C, GL1500, and now the Strat. Not bad for fifty bux and I'm not adding top heavy to a beautifully balanced machine.