Probably you are right. But if you have hard cases maybe you could consider finding a way to attach the time to the case itself, perhaps drilling 2 holes at the back of one of the 2 and have the tube there. Just an idea but it will depend on the shape/ material of the case and on whether or not you are willing to make such modifications to them.
Sure, hose clamps are strong and thin, but then you need to find a way to make them catch onto the tool tube 'lips'. Maybe cutting 2 small slits in the tube 'lip', with a heated flat screwdriver or something similar. Then you can have a hose clamp passing through them and around the panniers rack. Just an idea, I am not sure how solid it would be.
