as much as I like the Tubus Cargo I'd suggest a rear rack with lower rails. It makes a big difference for attaching/removing panniers or things sitting on the rack when the panniers can sit seperately from items tied on top of the rack. I'm not familiar with a Tubus Cosmo but Topeak makes a dual rail rear rack that works well. If I get groceries with the Cargo and Ortliebs and want to get a bag of charcoal I'll have to put some paper or cushion over the Ortlieb clips or they'll tear into the charcoal bag. Same thing with a rack trunk when I get to where I'm going I can't remove the panneirs until what's strapped on the rack is removed. With dual rail racks you can leave what's attached to the rack and remove the panniers