Enclosure is mostly to keep cat hair off my printer (my cat sheds like crazy) and to filter some of the microplastic dust and fumes. It does reduce warping by keeping the volume warmer than room temperature, I print a lot of PETG so this helps.

Dang, I need to try that. Good idea.

It might just be the specific spool/brand of PETG you used. Try buying some from a major well-known manufacturer, like Overture, Polymaker, etc. I’ve had cheaper brands shrink, warp, have adhesion issues, and all sorts of other quirks.