I can see your logic and i can see Fribbtastic’s objections. I am not sure immerse in a liquid a suction cup will be necessary. I would start out with a 20mm cube. A pure flat surface right in the middle of the filament where you’re going to get the most flex of the film.
I would sincerely consider giving your film 50% slack for eventual failure and loosening but your idea is sound. I do think commenter is right though that this would be something to redo on every single film replacement AND every single resin you use.
I’d genuinely be curious to see time saved VS used up to dial it in.
Let the players as a group have agency in your narrative. It sounds like a stupid joke about the pet goblin but it isn’t. Our favorite campaign ever was a mage campaign where the players spent the whole campaign focus on one guy (Sir ben kingsley in Lucky number slevin) and they went after him with all they had. But on the side they made friends with some of the factions. Especially this one Sons of Ether, Lucy Monk. They confided in her and had her help them with plans. it was great.
Then the twist came.
Yeah, you figured it out.
But the look on their faces when they had to travel back in time to get the guy they thought was the BBEG and he turned around and showed them who it really was still makes the DM giggle to himself.
Any game you play matters if the players feel they are moving things along and making a difference, even a small one.
If you are the DM, be the rest of the world but let them move you.