With through-bolts and a backing plate is the simple answer. If you are putting it on a curved surface, make sure the back plate follows the curve, either by shaping a piece of wood or metal to mirror teh curve, or using something with a litlle flex, like 1/4" plywood or sheet sluminum.

Remember that if the surface you are installing he rail too isnt sturdy, the sturdiest installation isnt going to be worth much, understand? There may not be a grab rail where you want it--I'm guessing the side panels--because these are somtimes little more than trim pieces.

G'Luck
Kevin