Use a good spray adhesive, like 3M, and insure you don't get it anywhere you don't want it. When fitting your pad, get help to maneuver it into position where you want it before pressing the pad down into the adhesive. Once down, it's not going to move. Use a plastic or wooden tool to work the edges of the material under the reinforcement under the bonnet/hood. It looks really nice and neat if you can get the pad centered between the reinforcements and then tucked neatly under them.
Scott Stuchell