How do I print structural things (cup holder, pin, etc.) for the inside or outside of a car?

• standard PLA is out: heat sensitive
• there's ePLA and PLA+ and other special PLA that claims to be more heat sensitive. Reviews are sketch and brands unrecognized
• ABS would require printer modifications
• PETG might be a reasonable compromise?

• PETG on Ender 3
• PETG settings on Ender 3 V2/Pro tl;dr no fan, bed at 60*C

Whatever material used, it seems the annealing process will be important

• method for annealing: tl;dr use sand and a toaster oven
• annealing experiments: tl;dr 110*C for PETG
  • While the Prusa blog above shows some evidence that annealing helps heat resistance for PETG, CNCKitchen on Youtube shows more compelling evidence that annealing is not effective for PETG without seriously warping the piece.
• CNCKitchen shows compelling evidence that annealing in plaster greatly increases heat resistance in PLA and strength in PETG

Because of warpage and the contradictory evidence that this helps in any significant way for heat resistance or strength this process may not be worth it