Should you need to use the 3M adhesive mounting pad in place of screws you need to clean the area where the unit will be mounted.
Make sure there is no oil or dirt for a maximum hold. Use alcohol if necessary and let it dry completely before mounting. For best results peal one side of the pad backing and place it on the bottom of the unit. Then peal the other side and position the unit and press down firmly.
Make sure of the positions before you place it, as it will be difficult to remove once placed. IF you need to reposition do it quickly before it starts to bond.