I've successfully drilled into the brake bridge of a vintage frame. Drilled like butter.

I thought about the water bottles, too. I am not willing to drill into the down tube.

You probably should decide how good a frame it is. The best frames were double butted and thin in the center, so I wouldn't drill those.

That said, 'silicone' what?? Cement?? I have the clamp-on bottle holders. Haven't figured out how to keep them from sliding, especially around and around!