Check the SCICON line of saddle bags with the roller mount system.
I have used them in the past and like them a lot. I no longer use a saddle bag, so I don't need to use my SCICON. One of their best feature was the fact that one can easily move them from one bike to another. Another great feature is the absence of straps to damage bib shorts.
For those of us blessed with sprinter thighs, saddle bags with straps can quickly chew through most bib shorts.
https://us.sciconbags.com/saddlebags-frame-bags