I found that the bungies just do not work. I picked up some short (about 18") cinch straps at REI (like the kind that go around sleeping bags) - they go through the rear tie-hooks, and around the shelf. Work great, plus allow you to let the shelf down as much as you want without having to hold it.
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- Grumpy Tom
http://www.grumpytom.com Unbreakable toys are useful for breaking other toys...