The famous System Saver from Kensington Microware has a well know issue where the fins that hold it to the Apple II case will break eventually.

This model is a replacement plate. The fins are pegged into the plate and held by friction (needless to say, you need some percussive persuasion to get them inserted fully - I used a hammer) Should one break, you can always replace it (although it might be difficult to remove), or reprint the entire thing.

The model is available on OnShape.

Thank you Scott Whitney for the outlines.