3M HD double sided tape on mirror, mirror clamps on all side of mirror. Usually don't have to put in rivets or plastic plugs.
Heavier items I use the metal expandable anchors using a special tool to expand them so the anchor doesn't turn in the thin wood.
'16 Outdoors Timber Ridge 280RKS
Reese 1700# Trunnion w/ DualCam HP
'03 EXCURSION XLT V10 4.30 Axles