Yeah, I started a thread on that possibility recently, major problem being the construction of the tubus logo rack I use doesn't lend itself to this. Not enough frame to get a grip on. You can just about strap it down to the top of the rack using toe straps as someone suggested, that might even have been you
@mjr !, Sadly, toe straps are not as convenient as I had hoped. You have to use some force and spend a minute or so positioning it all to ensure it is secure and doens't rattle so it's not as convenient for quick stops at the shops, that's why I was looking for a permanent fixture on the frame.