Thanks for the reminder, I'm a flake
It's pouring right now, so no pics of how I have it mounted, but here it is from above.
To mount it to the rack, I used a basic u-shaped threaded rod and a big-azz wingnut. It's been up there for a long time, no major issues except gas mileage (or lack thereof). I don't think it's that hard to get up and down but I haven't taken down in months and months.