We had a similar problem with our R&M rear racks which were MIK. You could either use a trunk bag or panniers, but not both.
Typically we wanted to use both, so I added some pannier rails using the following two methods.
Rubber lined P-Clips to fix the rail to the rack.
View attachment 165069
View attachment 165070
Crimp lugs either end of the rail to bolt on the rack.
View attachment 165071View attachment 165072
Both methods now allow us to use panniers fitted to the lower rails and a trunk bag to the original rack.
For information, we use Ortlieb panniers and trunk bags, which fit nice and securely to the bike when we are trekking on roughish cycle tracks.
DG…