LOL, the sheet metal on modern vehicles is so thin that regular NMO mounts barely can clamp without dimpling, not to mention seem like they'd bend up in a stiff breeze.  So I reinforced the underside of my roof with something similar.  I ended up using a little bit of conductive epoxy rather than tape, though.
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A side note about mag mounts.  I get why you used the clear tape but it's dirt and grit working its way under that cause the damage.  It seems solid but they actually vibrate and rock a little with the whip, it's like a little disc sander.
So you probably should periodically remove the mount to clean it regardless of the additional film.  They aren't really designed to be a permanent mounted thing so there's no attempt to seal them from doing it.
Maybe, if I understand, the way you've done it (adhesive down?) will be better.  But even that, I dunno.  I have 3M clear on the leading edge of my hood that looks like crap now 10 years on from when the P.O. put it on.  It left a dulled surface when it started peeling and has to be removed that isn't much better looking than the rest of the unprotected hood that has had regular washes, touch-up and wax.  I'm not convinced it helped in the long run.  I suppose it did prevent rock chips, though.