How to mount mirrors on thin walls

For towel bars, I made up some backing plates of thin (1/4" or 5mm) plywood that I glued to the surface of the wall, and then used typical plastic expanding anchors that went through both the wall and the backing plate. The glue is mainly to keep the plates in place during installation, rather than as a primary means of support; the plates serve both to help distribute the stresses on the wall (i.e. help keep the towel bar mounts from puncturing the wall material) and add enough thickness to let the anchors grip properly.

Easing the outer edges of the plates with a chamfer bit in a router and painting them with enamel, they look something like blank electrical switch plates under the mounts. So far it seems to be working very nicely, but I don't have enough use on them to give a long-term report.

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.

I know my manual says to use pop rivets(but be careful drilling)Hung another towel rack this way works fine