Well, I solved my quandary re storage space. I installed the Givi S220 Silver (I think that is the model). First the good: great quality, nice looking, plenty of storage and a good fit. Now the not so good: not easy to follow the directions no matter what language you speak, they pretty much eliminate the trunk use when installed.
The one main drawback for me is that after you receive them they say that you need brackets (which as far as I know, are not made for the DT 300. Unless you want to rub the paint off the sides under the saddlebags, it requires some modifications. I have some gasket material for sealing the cowl on my El Camino. It is flat on one side and rounded on the other. I glued the flat side to the back of the saddlebags. They stand out from the fender just enough that they don't they don't rub and the gasket is rubber so it does not move.
Hope this helps anyone looking into getting saddlebags.
