I just got done permanently fixing the "always blowed flat against the door" passenger-side mirror on the wife's truck.
I had previously tried several short-lived remedies, only to have the mirror swing flat against the side of the truck, when I, or she, needed it the most.
Here is what I did, and it's guaranteed to buckle the sheet-metal before it gives again.
I drilled a 7/64" hole through the thin metal clamp that holds the mirrors shank.
As the shank is too hard for drilling, I marked the hole location on the shank, after the wife assured me that the mirror was positioned like she wanted it for now and all time to come.
I took a diamond-pointed cutter in a Dremel tool and cut the hole in the mirror shank to 3/16" diameter, being careful to not damage the power-head operating wires.
When I re-assembled the mirror, I drove a short #8 hex-head sheet-metal screw through the clamp and into the hole I cut in the shank.
To further secure things, I drove another screw in the crack between the shank and the aluminum bracket, as far as it would go, then cut the screw-shank flush; this really tightened things up.
I re-installed the trim/cover.
Nothing short of a solid gate-post, or big Beech tree, is going to move that mirror now.