Prorack roof rails?

I need a car top carrier for a one time trip to carry a little extra capacity and was looking into getting roof rails to help anchor the car top carrier. I know some of the soft "bag" carriers don't require roof rails, but I'm worried about the straps interfering with the side curtain airbags. The Thule and Yakima roof rails are pricey considering I'd only use them a handful of times each year (I'd remove them when not in use). Has anyone had experience with the Prorack rail system? Is it a decent alternative? It's about half the price.