I used a pair of climbing nuts that looked good and will not come off!

http://climbing.about.com/od/climbingequipmentwords/a/NutsDef.htm

I looped them to the luggage rack so that when the rack comes off so do the spring pins but they stay with the rack.

One less thing to worry about.

What's your mileage? Who cares. Is it practical? See #1. What happens when it rains? You get wet.