lkchris

Of course the Mercedes crossbars are designed for the T-track system and it's likely your Thule roof box features a clamp system ... which is just fine.

However, FYI, Thule does make adapter kits to convert these boxes to the T-track system, as shown in the attachment. These kits must be ordered from Europe as of course Thule USA doesn't stock them. Your Mercedes crossbars are the 20mm size

Also available elsewhere but not in the USA is a fitted luggage bag that fits nicely across the nose of your roof box. Part # 8001. https://roofracks.co.uk/thule-gopack-nose-bag/