Originally Posted by bradv
If the manufacturer had installed it, they would have used screws.
You may be able to use sheet metal screws, but I think I would drill and tap the trailer for machine screws (the metal should be pretty thick, a little too thick for sheet metal screws).
If you're worried about corrosion, spray cold galvanizing paint on the area after you drill and tap the holes. After it's dry, install the pads using a good sealant on the screw threads.