Yea, rock rails, just used the GM baptised name.
I have dealt with GM Parts Direct before, and on some items, their shipping is ridiculous. Whereas most places take into consideration the quantity and lower the shipping price, GM parts direct, puts a shipping price on each part, and that adds up with the order. (Example, purchased four calipers from a Montana dealer for a Vette. The price of shipping was 10 bucks each, but only 15 for the entire order of four. When priced on GM parts direct, they added the 10 bucks for each caliper; thus the shipping was 40 bucks. That is why the Montana dealer got the order.)
However, on these GM accessories they do not carry in stock, I'm assuming they are adding a $9.95 handling fee, and ordering via GM accessories which drop ships the package at my house. If GM parts direct order the GM accessory, the price from GM includes shipping. So it appears in this case, ordering these parts from GM Parts direct might save some pretty good money.
Their price for the rails is $470.92, for the undercarriage protection it is $289.10 and all they show is a $9.95 processing and handling fee. I wrote them and their first reply was worthless, but I addressed their first reply and surprisingly, I received a decent reply. In the second reply, they implied that the shipping was part of the order from GM, and the cost I saw, was what I would pay.
I priced rocky road rails and they were $472.86 shipped, and then from H2Parts the undercarriage was $426.20 shipped.