Silicone sealer (RTV). Put a dab on the back of the panel (right on the 3-M tape is fine), and stick in the appropriate position in the receptacle. Take a folded paper towel or something, and put between the cover lens and the panel to hold the panel in position (OBVIOUSLY don't turn the light on while the paper/whatever is between the panel and the lens), and snap the cover lens in place. After a few hours, the RTV will be cured, and the LED will stick in place. Remove the paper. I've done 10 LED's in my RV this way, and it works EVERY TIME.