All on the inside. the only thing that you will have coming out of the bottom is the 4 square bolts that slide into your rails. So metal plates then plastic then the fasteners.
Peace
-Eric

Hello,

I just bought one of those Hummer Cargo Boxes (The Last one GM had in stock).Anyways, it was missing the instructions!

Do you put the metal plates on the outside of the box or put the box on the roof, then the metal plates (in the inside of the cargo box), then the plastic piece with the fasteners?

Thanks & Regards,

Jeff