Help me mount my mount...

[Sodium Duck]

I have these antenna mounts that I want to put forward of my mirrors. I took the A-pillar off and unfortunately, there's no access to inside unless I drill a big hole in it which would probably be a bad idea, structurally speaking.

I think I could use some self tapping metal screws, but I will probably have to take these mounts off and on every once in a while, and I think over time it'd get worn out and stop working.

Does anyone have an idea for how to get this screwed to my car? Some sort of screw/fastening system/etc?

I would really like to get a T-nut and spot weld it into place, but I don't have a welder or know anyone with one. That would be ideal though. Any other ideas? Maybe JB Weld to hold it in place?