FWIW, I used 4 rivnuts a couple years ago for water bottle mounts on my 531 Reynolds Raleigh Competition. At the time, I could not locate any decent quality clamps.
No problems so far, drill bits took ten minutes or more for various drill bits to penetrate each hole that really tough steel. That stuff is STRONG.
I epoxied the rivnuts in, so the bike's Reynolds tubing has
some support and reinforcement on the edges of the drilled holes. Plus each hole itself is occupied by a water bottle screw, filling any void in the metal. I would be highly surprised if any of these holes form cracks, but stranger things have happened. I'm not sure I would go this route again, and if i did, I would take more care in locating the holes,. Unfortunately, the steel tubes make it difficult or impossible fit a to drill in certain spots, making the project a rather unpleasant PITA.