I have a large Acorn saddle bag that I mount on my tourer from time to time. The tourer has a Brooks saddle. I use the two metal slots on the Brooks and the seat post as mounting points. My road bike has a lightweight Fizik saddle with no slots.
There have been occasions where it would have been nice to use the saddle bag on the road bike. I use a bar bag on that bike sometimes but space is very limited.
Seems like I recall something about a fixture that attaches to the seat rails and has slots that allow for the threading of the bag straps.
Can anyone help?