I need ideas to hold my mirror glass in "canister"

So I just got 2 runabout style mirrors from LostSouls sale, and the mirror glass dosnt seem to be held in to well (it didnt come off during driving but I dont wanna take any chances).

I would like to use some sorta "rubber caulking" to seal the outside edge, I am sure before I go out and buy something that if I post on here I will get a much better idea to how to fix this problem

Help is appreciated