I have the Saddlemen Tunnel Bag, I bought it about 8 years ago for a different bike. It's done plenty of miles in a range of weather and has held up very well. We get the Tracer here in Aus with the panniers included in the price, I just don't always need that much space or need to carry that much weight around. The bag fits like it was made for the Tracer and holds plenty for one or possibly two day rides,
it doesn't really expand, not like a double zipped suitcase anyway.
it's not a big top box, it's more an alternative to a tank bag I guess, I think it holds about 22 litres which I think converts to .75 of a cubic foot, is that even the right conversion? Had I remembered I still had this I wouldn't have bothered buying the tank bag.
here's a couple of shots where I've filled it with some towels to better show the size, I usually have some water bottles, a few snacks, a tyre repair kit with mini compressor, thicker or thinner gloves opposite to what I start the day in it.
smifff I don't currently have oem luggage so don't know, are they possible to attach with that tailbag on? That would be a deal breaker for me. Do like the d-rings on top. Would be nice for a bedroll and hammock. *otherwise might be sold on that sw m.