AdaRac + Rolltop or Folding Bed Cover?

I called AdaRac hoping for a list of compatible bed covers, but no-go.
Is anybody successfully using AdaRac racks (http://tinyurl.com/3cau6jt ) with a rolltop or solid folding bed
cover?
Seems like AdaRack's rail assemblies would have tb stacked on top of all the covers' rail assemblies that I've see so far.
For definition purposes:
http://tinyurl.com/3o9p2zs (folding solid)
http://tinyurl.com/3krzhl3 (rolltop)
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PeteCresswell

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