@Damobius as an update, I’m just about done with another new sky camera. I say almost because the gorilla glass phone cover I used looked good, and I had the film-protected side up (so I wouldn’t spill glue or silicon on it) which I’ve now removed and discover it’s got a sticky something on it that I can’t get off. Lesson: film side down, I guess. Anyway I have more arriving next week, so I’ll replace it with something less gunky. Images show my new design enclosure. The block inside on the bottom is glued in place, but 2x sided foam taped to the camera mount so I can remove and fuss with it if need be. The Pi is rubber banded to a little riser I made, just in case water gets in.
I assume there's some sort of adhesive on the phone cover that holds it to the screen? Maybe the stickiness you experienced. I wonder if attaching it to a thin (1/8" maybe) sheet of acrylic? Not sure what that would do to optics though.