This post is a little late, as I did this work back in November 2009.
One of the things I look for most in a bike is overall practicality. A large factor in this is the ability to carry *stuff*. Sometimes LOTS of stuff. My last three Harleys had fairly large saddlebags and a huge trunk. More importantly, the trunk had a luggage rack on it that could handle a ton of *stuff*. The bike could handle the weight as well. I used the bike like a Pack Mule. There were times we were traveling down the road looking like the Clampetts (think Beverly Hillbillies). When we went to Florida from New Hampshire with our camping gear and SCUBA gear, all we needed was a rocking chair on the back with Granny sitting in it.
So, when I got this bike, I was concerned that we would not be able to carry as much. The saddle bags are bigger than the ones on the Harleys, but they opened from the side so are harder to really stuff. Zippered bags takes care of a lot of that. But I needed a trunk. My girlfriend needed a back rest anyway. You can load a ton of *stuff* on a bike with just duffel bags and such, but for any real convenience you need a trunk.
I found the E55 MAXIA 3 from GIVI. This Italian made trunk holds 55 liters. Pretty big for a bike, but the Harley trunk was 63 liters, with a lot larger luggage rack. The GIVI is a very well made product. Not as solid as the fiberglass Harley trunk, but it is a lot lighter. It also has a much lighter rack. Only two bolts hold it on. I find this rather scary, but I have not heard of many problems, and I have broken the mounts on the Harley. Of course, the Harley trunk was overloaded by about 70 pounds, and that was an old style mount.
The back rest on the Harley is large and wraps around the passenger to some extent. It is rubber mounted to reduce vibration. It also adds a fair amount of weight to the trunk. The GIVI is only a small pad, but my Girlfriend likes it well enough, so I suppose it is OK.
There are cheaper trunks out there. They are lighter, but cheaply built. More than good enough for most riders, but I felt that with the way I was likely to overload it I should get the best. Not sure if it will make much of a difference in the long run, but this trunk can be mounted on almost any bike, and it comes off with the press of a button.
This trunk went on easily, as shown below, and works very well. I am happy with this and use it continuously. Some riders say that this makes the bike unstable in the wind behind trucks and side winds. I notice only a slight change, but with a bag or a passenger on the back seat the bike seems even more stable than without the trunk.
Of course, after evaluating the situation, I still don't have enough room for big trips with my GF. I have decided to get a trailer for the bike. That will have to wait for another post.