passenger mirror

I'm adding a passenger side rear view mirror to my 74 convertible. Are there any blind fasteners that work well to secure these mirrors? has anyone had success mounting one?

It should come with a mounting kit that includes the 2 well nuts.  They are the rubber type that bulge as you tighten them.

Thanks , not real fond of the rubber wellnuts , looking for something a little more substantial so there’s not so much wobble. Maybe something all metal. J